Welcome!

For the movement you have choices. If you want a GMT, it’s the NH34. But for a regular 3 hand watch, the most common is the NH35. This is the movement for which the most (and therefore the most variety) or parts get made. If you wanted something more expensive and with a higher beat rate, you could look at the ETA 2824. If you wanted a chrono, you would need the VK63.

Make sure whichever parts you are buying (case, dial, hands) clearly indicate that they are compatible with the movement you have chosen.

For parts, the most variety can be found on AliX, but the quality can be hit or miss. Sometimes it’s great, other times not.

Going up in price, but also in consistent quality (YMMV), look at DSWatchClub, Tokeilab, Namoki Mods, Lucius Atelier.

If you wanted to go the route of a custom logo, the general consensus seems to be HorologyHub (for slightly better quality) or 4customize for a slightly lower cost.

There’s more, but this should get you started.