Not too sure what I should aim for next

you alredy have most of what you would need for camelot really. not going to spoil anything, but you have your base "covered" as long as you invest in the servant you have posted.
On the side note, i cant see mash in this list, have you forgot her or you have not enanched her?
if not, you should consider to!, she is easly one of the best servant in the game for hard content, i basically never taked her out of the team in camelot.

anyway, camelot is a wall. Is meant to test master and force them to be better with team and strategy, even the best servant in the game if not used correctly is not thet usefull.

if you are looking for good servant to summon, i would say skip the actuall banner. not thet they are "bad", but they are not good eighter.

there should be a class banner next month, and also the gudaguda banner but i would wait for the extra ccc campain, becouse ther you will be able to get many incredible servant (gilgamesh, tamamoe no mae and nero bride), and fragment of 2030, one of , if not the, most broken CE in the game will be on rate up.

Nice to see someone else who also plays this for the exact same reason as me lol, but like Exa said you've got a good line up so you should be alright and raise mash if not already done, this games fairly easy most of the time and even when its hard with supports it aint difficult to overcome , id say get anyone you like otherwise gameplay wise I'd recommend saving up for merlin or waver, waver will make your life a lot easier farming and in general and merlins just amazing, having them will mean you can use whatever servant you want from your friends list majority of the time and not having to rely on your friends merlin/waver, or you could go for gil who's a great boss killer and farmer who's coming up soon in the ccc event summon and the CE's Exa mentioned

In addition to what's already been said, you really can't go wrong with Casters as the premier support class.

Waver goes well with any team and is good for daily farming and hard content both. And, even if he is easy to get from the friend list, actually having him will open up options for you by running double Waver or Waver+Merlin. It also let's you borrow a DPS from whichever class you need for any given fight in case you don't have a strong or decent enough servant for the job.

He'll be on rate-up during the Chaldea Boy's Collection next month but he'll be sharing it with the other male Servants so it's not a very likely bet. Although the other male servants aren't that bad (Cu Alter and Ozy come to mind among others).

Merlin is, in a word, broken. He makes just about everything easy when used properly and with the right team (as mentioned, even the best Servants are pretty much dead weight when used poorly). He'll be on rate-up later this year if I'm not mistaken, so that's a lot of time to consider whether you wanna roll for him or not.

Tamamo is another great Caster but mostly for Arts-centric Servants rather than all-around like Waver. Though she could still do well enough as a healer/NP battery for a Buster or Quick team.

Medea Lily is still one of the best healers in the game, though I don't think she can be summoned outside the Story Summon unless she's specifically mentioned to be in a given banner (not too sure though, could be wrong).

Other than that, you're mostly good to go.

Looking at your Servant list, I can definitely recommend a few Servants that will greatly boost your lineup.
1. Euryale. There is no Servant better in the game at nuking high-level MALE bosses than Euryale. And the best part, she is only a 3*, so definitely aim to NP5 this kawaii Goddess.
She definitely has her own niche in the game, as there will be a lot of Boss nodes or Challenge quests later on in the game that will be made much easier having her around, ESPECIALLY in Camelot.
Her NP does DOUBLE DAMAGE to Male bosses and Servants, making it possible to even one-shot some Bosses with a 200k+ NP. Even if it doesn't one-shot the boss, her NP also has a charm, which is basically equivalent to a stun.

2. Merlin. There is no better Support servant than Merlin. I could write an essay about the benefits of having this Incubus Troll in your lineup, but I'll spare you the reading. I do believe that he will be available towards the end of the year in a banner. I forget which one though.

3. Lancelot. I find it good game-sense to have a Servant in each class that has a Single-Target (ST) Noble Phantasm (NP) and another with an Area of Effect (AoE) NP.
Nero, Sieg, and Rama all possess AoE NPs, and you will definitely find it useful at some point to have a Saber with a Single target NP, and Lancelot fits the bill. You can read his analysis here:
https://grandorder.gamepress.gg/servant/lancelot-saber#analysis
He has the potential to be equal or even better than 5* Saber Servants.

4. Hercules, a 4* Berserker. This guys survivability is legendary in FGO, especially if you get get his Bond CE, which unfortunately will take a long time to grind. As a Berserker, his damage is also pretty good, and is definitely a good Servant to aim for without breaking the bank too much.

Honorable Mentions (Most are 5* Servants, and will require a lot of SQ to get unless you are incredibly lucky).

1. Waver (Zhuge Liang). Top 2 Support Servant in the game, along with Merlin. He does almost everything, and is great for charging team NP gauges.

2. Jeanne de Arc Alter. One of the most reliable Servants to aim for if you are looking for damage. She has one of the, if not the best Attack Stat in the game, and is one of the games top Buster Critical damage dealers.

3. Gilgamesh. He has a powerful AoE NP well-suited for farming and ST dmg due to a majority of bosses in the game being Servants. Additionally, he performs well as a Buster Critical Damage Dealer thanks to a combination of on-demand Critical Absorption, high natural Critical Damage, high base stats and the ability to do Buster Brave Chains.

4. Carmilla. One of the games most reliable 4* Assassin servants. The main reason for this is her NP, which has a built-in ATK up and is extremely effective against female enemies. Her NP also includes a heal. Thanks to Carmilla’s first skill as well as her good NP gain stats, she is able to spam it rather reliably, allowing her to deal considerable damage consistently. Her third skill provides additional critical stars for the team and applies a huge critical chance debuff to an enemy, which although situational, is useful against certain Rider enemies such as Dragons.

Sounds like you could use some good assassins and extra classes.

There is going to be a class based summining campaign soon and they group assassins and extra classes together. You might be able to get someone like Carmilla (Assassin) or Gorgon/ Hassan Lobo (avengers). If you are REALLY lucky you could get Jack the Ripper (assassin) or Jeanne (Ruler) two of the best characters in the game.

https://grandorder.wiki/Class-Based_Summoning_Campaign_2

Based on what you have, focus on levelling Euryale (for Gawain), Nero (for final battle) & Da Vinci (since she isyour only 5 star).
Level Mash when she ascends too.

You are lacking riders, assassins, berserkers. Luckily, that will be remedied by free welfare servants Chacha, Kintoki and Scathach (assassin) later on in the year. Maybe you can get aim for a 5 star lancer too (useful later on). There aren't any welfare lancers as far as i know.
Bwt, thumbnail photo and actual photo seems different when i click on it. In your case, i might aim for Jack and say, Tamamo (lancer) or Scathach (lancer).