Any help to improve my composition

Hey Corgi,

First i feel sorry for you : Altria is probably one of the worst servant in this game (especially for a 5*) except for her NP. In order to use her correctly you need to push Mash with her and not Emiya. Emiya is not that bad so you can still keep it in your team. Cu is a great choice (even more if you are a free 2 play ). Well i don't know what servants do you have so i can't make a proper team for you right now.
Your CEs are good except for Altria, would be better if you have Verdant Sound or Imaginary Element.
For the skills :
https://grandorder.gamepress.gg/servant/altria-pendragon
https://grandorder.gamepress.gg/servant/mash-kyrielight
https://grandorder.gamepress.gg/servant/emiya-assassin
https://grandorder.gamepress.gg/servant/cu-chulainn

Level cu, Grail cu to 90, and level protection from arrows to skill level 10. Take care of your doge and your doge will take care of you. Mash is good as well and Hans support when you get them. But doge is best doge and the solo roach king

It is hard to tell without seeing what other servants you have. If you are new, seiba is most likely your best saber so keep raising her. She will also eventually get a strengthen quest, but if you have another saber like lancelot or rama, use it instead. Emiya and cu are great as well. If I wanted to complete this team with a 5th servant I would choose hans for sustain, crit buffs, and star gen. He is easy to obtain but requires leveling his skills. Also look for a strong rider like ushiwakamaru and an archer like any archer in existence. As for skills, try to raise them up to 4 for the skills they need ie not instinct. CEs really depend on the team but for now it seems you should lean towards an arts crit team.