Servant recommendation

Given that you're F2P, I think the most important thing for you to do first is to incorporate 1-3* Servants in your gameplay. Quite a lot of them can do the job of 4-5* despite their low rarity and some can do things that no 4-5* can do.

I'll edit this later for more details (unless someone else does it for me first) since I'm short on time but here's a brief list of the more useful 1-3*s.

Caesar, Bedivere, Euryale, Robin Hood, David, Leonidas, Cu Chulainn, Prototype Cu, Jaguar Warrior, Georgios, Ushiwakamaru, Medea, Hans(!!), Cursed Arm Hassan, Kotaro Fuuma, Asterios.

The others not on the list can still be useful in their own way but these are the most commonly mentioned as being worth leveling despite their low rarity.

If you're asking about rate ups, I'm assuming you're looking for 4 and 5 star servants. Considering your units, I have three recommended summoning campaigns.

First, with an estimated release date near the middle of April, the Fate/Extra CCC pre-event campaign. The specific servant here is Tamamo no Mae. Your Lancelot, Vlad, Kuro, Jeanne, and Nero Bride synergize well with her to make offensive teams focused on spamming NPs, and defensive teams. Tamamo support is commonly found, but having powerful support units like Nero (Bride) and Tamamo, will often open up your options in choosing offensive friend supports. This campaign has two days where Tamamo is the solo rate up. Also, this campaign also has some valuable CEs, specifically Victor of the Moon, Another Ending, Devilish Boddhisattva, Fragment of 2030, Knight's Dignity, and Ideal Holy King. Alternatively, Gilgamesh also has a solo rate up during the campaign, but you may have mixed results with him considering much of your critical star generation comes from skills or NPs.

My next recommendation cones directly after the last. The SE.RA.PH event comes with its own summoning campaign, featuring Meltryllis, Passionlip and Suzuka Gozen. Meltryllis has somewhat decent star generation with her stats and hit counts, and with her ability to generate stars on demand, can work as an attacker and star generator. She also has the somewhat rare ability to remove buffs, increasing survivability against some enemies, particularly in conjunction with her evasion and NP damage reduction. Passionlip is a more defensive option, with an AoE NP that also heals, taunt ability, and self-defense buffs on all three of her skills. While she does not have evasion or invincibility, her skills make it possible for her to tank some single target NPs on her own. She can also raise her own attack by a significant 30% (though this skill will also stun her for a single turn), ignore invincibility, and her skill strengthening in the somewhat distant future will add on another 30+% if her health is below half. Lastly, Suzuka Gozen. Requiring more support than the two alter egos, she can still pack quite the punch, particularly if you can set up a Buster Brave Chain with a decent amount of critical stars. Her NP is an AoE, causing some damage fall off, but its overcharge effect grants her a significant critical damage buff for three turns. Her buster steroid also doubles as a critical generation buff, giving a slight refund in critical stars, even after a Buster Brave Chain. While she has no personal defensive skills, her charm skill doubles as an attack debuff. Finally, her 3rd skill provides NP generation over time, while buffing her NP damage by 20% on all levels.

The third campaign I'd recommend may start in less than 2 weeks, with the rerun of GUDAGUDA Honnoji. The specific servants are Okita Souji and EMIYA. Both of these servants work as critical star generators, Okita with stellar passive generation and hit counts, and EMIYA with one of the best critical skills in the game. Also, both have a critical damage buff, though Okita's is linked to her evasion. With Okita's hit count and high NP gain on attack, a NP gain buff such as Nero Bride's can see her recharge back to 100% after a NP brave chain with some crits and shukuchi skill. The ability to reload immediately deals massive single target damage from her own attacks, and any follow-up, with her NP lowering enemy defense by 30% for each usage. EMIYA, the nameless guy who actually has quite the list of names. Funnily enough, his NP being Buster seems to do him more harm than good, lacking the ability to do a single card NP brave chain. Regardless, while his star generation may fall short of Okita's, it can still stand on its own, and really shines against a wave of three. With more and more challenging content consisting of enemy teams rather than individuals, his high hit count, critical generation skill, and attack down debuff make his NP a welcome addition to many teams. With above-average star weight, projection skill, and triple art deck, he can also regain a large amount of charge with a NP brave chain. Also, with his evasion skill tied with a defensive buff, his survivability is quite good. With Nobunaga returning, both servants can work as critical star generators for her critical skill and as attackers in their own right. To warn you, this campaign also raises the rates for some 3 star servants you may already have.

So... I think I actually spent a good two hours looking up specific information and typing this up. Hopefully you have enough SQ saved to actually make use of one of these campaigns if they strike your fancy, assuming someone actually reads this monstrosity.

Gameplay wise, just go for support. Your comp is exceptionally good to play an Art team, Nero Bride, Saberlot, Vlad III and Jeanne are all good pieces in an Art based team, especially after Jeanne's buff coming in mid year. You should try pull for a Tamamoo who have a solo rate up in the CCC preparation banner which have 2 slots where she had a solo rate up. Its quite hard to use friend support for this one as normally people put Waver and Merlin for support. I would strongly recommend you pull for her, but just take note that Art team requires core skills to be leveled to be stable.
Waver is also a support you definitely should get but there are no solo rate up this year though there are events it shares rate up with Proto Arthur in the upcomming valentine event. I dont really recommend pull this as Proto Arthur is not a strong servant gameplay wise and it really lowers the chance of pulling Weaver.
Merlin, please get him, trust me, you wont regret getting him from the solo rate up in the alter part of the year from the 1000mil download campaign. For the next one and half year, this game is simply the playground of Merlin. There is no challenge quest if you have a Merlin, serious. He is just so OP that he simply does whatever you want in a challenge quest. I am not too sure if there is still chance to get him in future but it will be quite far even if there are.