How should I summon?

This game has very little power creep. The anniversary characters are often decently strong (and the strongest character in the game was the 5th anniversary servant), but so are a ton of other servants (the second strongest was actually released like a week after the 6th anniversary servant for a a main story chapter)

As for who to roll, I would recommend rolling for who you want (whether that's meta or gameplay or waifu is up to you) the game can be beaten no matter who you roll and the meta is for braindead farming clears more than anything else.

Ima be real with you chief

Do the friend point summon

A lot if the three stars are really good, and the current one star in rate up has the kit of a four star at minimum. Start with Hans as a support, he's really good at getting characters to crit.

What the other guy said is very much true, but There are some very strong supports that would make the farming much easier.

For Arts: Caster Artoria (Castoria) (she can also support pretty much any type but she does better with Arts)

For Buster: Koyanskaya of light

For Quick: Scathach-skadi (Caster), and her summer version which is coming this August.

There is also Zhuge Liang who will benefit you and help you a lot if you don’t have any of the above ( you can get him for free too when the game asks you to choose a free 5 stars)

Since you just started playing I would recomend you to make a few 11 roles in any saint quartz pool to get some garanted 3 star units.  

Once you have a few servants to play with you can wait and save quartz for the really strong ones.

If you go purely for meta, instead of anniversary wait for the summer event, you will have:

-Lady Avalon, a really good Arts support.

-Ruler Skadi, the best Quick support with a dash of Buster support too.

-Summer Ibuki, the best Arts Berserker. Summer Erice is also on her banner (who will be EXTREMELY good against enemy servants)

-Douman, a fantastic support for Chaotic Evil servants.