so who should i try to roll for knowing that this is my roster
Gramps in September-November seems like a good option since you’re lacking in high-end ST assassins.
But you have everything nicely covered, and can honestly go for anything you want. Furthermore, if you do feel like you need an Assassin, you can pick one with the SR ticket.
Alternatively, you could save for New Year’s and roll for Melt, who can fill that gap as well while providing more versatility. Then again, we’re also getting Mecha-Eli in Halloween.
If Foreigners pick your interest, go for either Abby or Hokusai.
IMHO, Jack the Ripper in November or Jalter in January.
Generally you want an AOE and ST servant in every class. The only ones you are missing are an ST assassin and an ST caster, a lot of the time people will recommend using a berserker for dealing with caster or rider bosses.
If you want then you can roll for Gramps or Jack as recommended above for ST assassin and you could roll for Illya for completion’s sake in August (although there are a lot of good banners around then).
You have a really strong roster though, you could get through the rest of the game with this kind of roster so even consider just rolling for characters you’re interested in. After all, happy waifu = happy laifu.