Team composition

Honestly, Mash, Jeanne, and Martha are pretty much enough to stall almost anything to death. If you have Hans, raise him too. Keep herc as a backliner and only use Tamacat for farming. Have her personally, and she’s not much better for anything else. Cu is also good for backlining.

Where are you at in story?

Some additional servant suggestions are euryale georgios and david.

Mash/Hans, Herc, and Support Merlin is probably the ideal setup if you want him to kill and survive + it will probably get you through everything if Mash's skills are maxed, Herc is fully lvled and you have friend with a maxed Merlin

You can clear everyday quests with this set-up, but I wouldn't recommend it for most bosses. Using class advantage will help you hit harder and survive longer; Berserkers are best for mixed nodes (e.g. the Enforcement Knights in Camelot where you fight a Saber, Archer, and Lancer in the same wave).

Generally the game encourages you to build different teams, depending on the class/enemy you're facing. It's not a "find 5 Servants, build one ultimate team" game. At the same time, the difficulty is fairly low until Camelot, so if you want to throw Tamamo Cat and Herc at everything, you do you I guess.