In my opinion, it should suffice. Though you should probably increase their levels by doing daily quests. In my EN FGO account I beat camelot with d’Eon being my only 4 star. This was before I rolled a lot with summon tickets. I did take advantage of friend support though. Raise skill levels on your servants if possible. Without events, pretty difficult due to needing to grind constantly for the acension and skill materials. Also be sure to keep Mash’s level up too. She’s pretty useful for survivability for your servants. Take advantage of friend summon too. Raising NP levels dont hurt.
For CE’s thats a bit difficult. Depends on playstyle. Be sure to read what the CE does and put them in the servants accordingly. For example, Mash can take a pretty nice CE known as Gudaguda poster girl. Probably missed the opportunity due to the gudaguda event finishing. The lesser version of it would be Halloween arrangement. Basically it allows the servant to be targeted, and due to Mash’s special servant type, you can take advantage of the target focus to let your other servants avoid taking damage. It’s not always wanted, so it depends on strategy and playstyle and how you use your servants.
Before summoning for a GSSR, I’d stock up on quartz. I’d summon with 200-300 quartz, but if I like to play it safe I keep 1000 quartz. Stock up on summon tickets too, I get really lucky with summon tickets and maybe you will too.
I’d aim for Merlin, Tamamo, or caster skadi. For archer Gilgamesh. For lancer Enkidu. Though to be honest, all of these are just options. In my experience, there isn’t really any bad servants, its just that some are better at things than others. If you can’t really decide, and im totally not bias at all, I’d go for Jeanne d’Arc Alter and Jeanne d’Arc. You will get Jeanne d’Arc Alter Summer for free this year in EN i believe, a 4 star berserker. And you will get Jeanne d’Arc Alter Santa Lily, a 4 star lancer during Christmas (probably earlier). Besides my obsession, I do have a list in my pc that ranks every servant from JP but unfortunately its in japanese so I don’t think you can take advantage of it. I tried looking for an English ranking and came up with this: https://gamewith.net/fgo/article/show/7858
For rolling during that event, any would be good. Though you should probably pick caster, as Merlin or Tamamo are pretty good servants to have. If they aren’t to your liking, I’d risk the chance to get Jeanne d’Arc Alter, but thats just my biasness. I’d roll for her, even with a NP level of 5.
Other than that, can’t really help. It really does depend on how your playstyle is. We all have one. Mine is a pure focus on Jeanne d’Arc Alter attack and survivability, as she basically destroys every target I face while the rest acts as healing/buffing/shielding. Surprisingly its very effective, only struggling against Moon cancer’s, which are super rare and I have Jeanne d’Arc to handle that. There really isn’t a standard way of a strategy other than picking servant class advantages. It can take a while to find a strategy you like, and because you’re new, just have fun. I wouldn’t really worry too much about strategy and such. Testing servants, testing different strategies, etc is probably the most enjoyable part of FGO for me, other than trying my best to find a way to make Jeanne d’Arc Alter stronger, how to always use Jeanne d’Arc Alter, etc. It is, unfortunately, possible that you will miss events that wont have a rerun. But i wouldn’t worry too much about it. Just enjoy the experience, and you’ll most likely find a strategy to your liking