What Units would work with my Units?

You should just focus on the good 3 stars and lower servants you're not at the point where you really need a specific 5 star to round up your team and most of the 3 stars are better than your 4 stars except maybe saber alter, not to say marie and d'eon are bad it's just they certain niches that aren't that useful in common play. You should just save for a character that you like personality and design wise, but if you really just want a good 5 star than just go with merlin at around novemeber to december.

Run Chevalier with Salter and save for Zhuge or Merlin. Salter's big problem is that she has no defensive skills, but since Chevalier can tank it defeats that problem. Zhuge is obvious, he has amazing np charge and attack support. Merlin is also obvious because you can break the game.

Jeanne alter, tamamo, amakusa shirou, ishtar, and of course merlin are all great servants to save for.

Develop your cu chulain or doggo and develop and level your Hans when you get either of them. As for 5 stars, 5 stars are legitimately hard to get due to their low drop chance for that matter getting all the 4 stars you'd want is decently hard.
A big mistake most people make is assuming that saving up enough quartz means you'll get the servant you want if you roll on a banner. A better way to look at it is start the game by collecting and developping servants and CEs then once you have a good amount figure out what comps you can make with them.
The story mode can absolutely be cleared with 2 and 3 star servants and there's plenty of YouTube videos showing this to be the case. The 5 and 4 star collection and receiving is just the fun part of the gacha and is rare enough that it's fun any time it happens.

If you want more specific info on the merits and demerits of different 4 and 5 stars definitely check out the tier lists on this site. Worth a look for planning of future teams. Most of their info is on point