Team Building Suggestion

The only change I can suggest outside of max levelling your 5 stars (both Tama lancer and especially archuria can almost solo non class disadvantage content) is to get a Hans and to level your mash. I'm not seeing a lot of good levelled up supports.

The busterzerker comps don't really need supports since you're trying to just chain buster cards anyway. But most standard comps use at least one support if not 2 along with one main dps.

For levelling order as well I'd suggest you finish levelling Chloe and level kintoki rider as well. Both are among the strongest SRs and require little to get up bring welfare and can serve as standins till you can get your SSRs up to max level. Mash is another easy one to level (and a support) as her ascension is tied to the story and thus needs no material.

So a suggested temporary comp (till you get stronger supports) would be:

Keep going triple berserker or rather with the buster teams in your frontline. Make your backline be the three welfare servants you have in scathach, kintoki rider, and Chloe. Swap mash in if needed for defense or to use better CE.

Eventual comp though would involve Archuria for most fights with a support Tamamo and your own levelled Hans (or a support waver or tamamo if you get lucky and get one of them), backline of mash, your highest dps, and herc.

Leveling Hans at the highest priority as SSR, as well as Mashu. No matter what team building.
Pick up one Berserker for the highest priority. Lets say Herc, and try to get max bond CE of him. Then next Fran or Lancelot. Your Berserker team will not be quite effective as time goes by, but Herc or Lancerlot/Fran are always shinning in different role. Pick up the one you like. Ibaraki and Cat are not bad, but you have so many berserkers, then..

Leveling Kintoki as you first rider. You wont regret it. Quick support? Before Skadi's coming 2 years later, normal critical support like Hans and Waver could also be great for Kintoki.

Art team is recommended because you have Arthuria and Kuro. However they are both archer. Then you can try Nero Bride and leveling Li Shuwen if you made decision for rolling Tamamo. The art team's core is always Tamamo. Normally a art team's composition is Arthuria/Kuro (or most servant with 2 Art card + Art NP) + Tamamo + Tamamo/Waver/Hans/Mashu/Jeanne, etc.

Off course, Waver is also great for Altera and SummmerTamamo. So it is a recommendation for you to try this class rolling of Casters since you are quite lacking of casters. Besides of top support of Waver or Tamamo, even Xuanzang may helpful.

If you want to rely on Altera as your first Saber or TamamoSummer as your first Lancer, then Waver and Merlin are always recommend. A normal configuration is Altera + Waver + Merlin, but dual Waver or dual Merlin still work, or even Hans.

If you still prefer to play berserker team, you can build Waver + Herc + high skilled Mashu + Fran/Lancelot, depending on different circumstances.

For assassins, Camilla and Shiki are decent. Versus rider, Shiki could be also support by art team (just please provide good protection to Tamamo and other caster support), but Camilla is more flexible may paired with other assassins. Unlike

Not really recommend to leveling any 3 stars except Fuuma and Medea. Even Cu and Euryale, you already have decent SSR and SR(except Fionn!), so... And David's second skill.

Oh, dont forget decent CEs

So far, you only have one support leveled up. Mash. Level up david, hans(if you have him), and eventually chevalier deon. Your dps lineup is heracles/ibaraki, altera, tamamo lancer, altria archer/chloe, medea, shiki/carmilla, and rider kintoki/ushiwakamaru. Both Cus fuuma and scathach deserve mentions as well. Lancelot, tamacat, frankenstein, and kiyohime should be leveled if you have multiple kscopes for farming. Build around altria archer in an arts comp. Have a backup team with altera in case facing lancers.