Welcome aboard!
As a GSSR2P (I give them $15, twice a year), the game is still very approachable. My account is in fantastic shape. However, you definitely need to have a lot of discipline on your rolls.
From a pure gameplay standpoint, the most important units to have are Support units. The big ones being:
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Waver -- who you already have, excellent generic support, also he's Waver and we love him. Notably doesn't
need
skill levels early on since his NP charges don't scale with them.
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Artoria Caster aka Castoria -- The best unit in the game by a mile, works best with Arts units but is just broken in general
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Koyanskaya of Light -- the dedicated Buster support, she's all-in but makes farming or nuking things down easy
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Scathach-Skadi -- the dedicated Quick support. Overshadowed by the other supports, but she gets a Summer version this year that is largely an improvement over her base form.
With good supports, you can make almost anyone work.
Of course, feel free to roll for love, but know that a ton of the silver and bronze units in this game are fantastic in their own rights. For example:
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Shakespeare -- targeted 20% battery and decent party-wide buster up for a turn. Pretty great for such a low cost, I'm using him in the current event's raid right now.
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Arash -- the king of clearing one (1) wave. He won't be fantastic until you complete jerusalem and get his NP upgrade, but his cost is super low and he offs himself on NP, letting you rotate in a backrow party member for free
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Spartacus -- Don't let his stats fool you, this guy is your de facto early-game omni-farmer. Farming is like 90% of the game by volume, so knowing who's good at farming is important. Just make sure to end fights kinda quickly since he's made of glass.
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Georgios -- STILL the best tank in the game. Even better than Mash when it comes to pure tanking. It's not close. Has a coveted 3-turn taunt (one of only 2 Servants iirc, the other being Percival, a 4-star), big DEF up, a guts, the works. You can even do Dragon memes with his NP if you have an anti-Dragon unit like Siegfried.
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Lu Bu -- He bonks things really hard. The stat stick by which all other stat sticks are measured. (I guess you have Herc already)
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Hans -- I'm not as high on him as most people, but he provides a wide array of buffs and utilty as well as healing. It's a shame 2/3 of his NP buffs are RNG.
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Robin Hood -- Robin is still my unit of choice to kill Saber bosses. Just make sure the poison lands.
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Euryale -- My unit of choice to kill Saber or Zerk bosses who made the grave mistake of being Male.
All of these are guaranteed to get NP5 eventually as you roll out your friend points. Most other units are workable as well. Just don't invest anything into Jekyl. He's awful and not even in a way that's fun for contrarians.
Herc definitely is not your best roll in the tutorial summon; Helena is since she's a dedicated support unit. Herc doesn't get great until you get his bond 10 Craft Essence, which will take months. He's still fine for now, and tutorial rerolling is not at all necessary in FGO. Plus you like FSN, so that helps.
As someone else said, Fuyuki is pretty good, and Orleans has cool ideas even if the actual prose is wack. Jalter is a fantastic character concept that keeps getting better once she's on our side. After that - I'll put this in spoilers in order not to skew your expectations, but if you want to know my thoughts, feel free to click:
The quality takes a turn for a while afterward. Rome is pretty bad, Okeanos is a mixed bag with a plot that could've been better, London is terrible plotting but crucial for worldbuilding and carried by a couple of characters, and America is a fun, if strangely executed, romp.
Then it hits Jerusalem and decides to get incredible.
Save your apples and/or spare AP for "lotto events." These are unlimited farming events that give you almost everything you could want: FP, QP, class gems, and a truckload of 5-6 specific materials. Unfortunately, the coming lotto is story-gated kinda late in the story from where you are, but don't try to rush to get to it and ignore the reason you're here: the story. There's no PvP elements at all, so don't feel pressure.
Finally, the game won't tell you specific numbers on the effects of skills or NPs, so get used to using the wiki a lot. Don't look at Gamepress's tier list though. It's memetically terrible.
If you want to add me, my code is 545,046,833. In-game name is Lance.
Enjoy!