Hey I’m new and need some guidance lol

Mash, Hans and Waver/Zhuge Liang. Anything else is supplementary.

I'm not even joking around. Pick virtually any other unit as your damage dealer(s) and support them with the servants I mentioned above.

"50% of the game" is relative. 9 months ago and I would have suggested powerhousing half of the game with Mash and Heracles only.
Now, though, including event participation as part of that 50%:
Mash Kyrielight
Hans Christian Andersen
Chloe von Einzbern

This Arts team will carry you through the game for the foreseeable future; they can be acquired easily, assuming you got Chloe from the last event.
Oh, and put Heracles at the back.

Mostly support in this game is pretty broken, also the strongest unit in the game yet and can clear the game by party of themself.
Also you can clear most content with just a single Chu lancer ( you'll find more later ).
The most recommended one is just take all servant you need regardless the rank or rarity. gold servant is a bonus, if you're F2P ( free to play ).
Have some cash or budget on, just look at the tier list from this site.

1-3 star servant can clear 100 % of FGO content, just use your servant wisely.

Out of the low-rarity servants, Mash, Hans and Cu should be your highest priorities.

If you got Heracles as your tutorial servant you can steamroll most of the early singularities, but you will eventually want at least 1 good servant in each class. I would recommend investing in the following 3* and below servants:

Saber: Caesar, Fergus
Lancer: Cu (original or Proto. Prioritize original if you have him)
Archer: Robin Hood, David, Euryale, Arash
Rider: Ushiwakamaru, Georgios
Caster: Hans, Medea
Assassin: Fuuma, Cursed Arm Hassan
Berserker: Lu Bu

If you don't have a good Saber, it may be a good idea to roll in the Nero Fest banner and try to get Caesar or either version of Nero. Due to the lack of 3* and below Sabers, unlucky F2P players can find themselves going for months without a good Saber.