Areas to mask when painting a bike
First up - consider buying a bike in the colour you want.  That will be the easiest/cheapest solution.

Anything with threads (internal or external) and anywhere that has flat machined surfaces for nuts/bolts to tighten against should be masked to prevent paint.  If you do paint surfaces like dropouts, the paint will crack and flake off quickly.
You should also mask off anything you want to stay chromed, and remove all parts like groupset, bottom bracket, seatpost, bars, stem, cables, etc.
The best paint job comes from a completely blank frame, so remove all decals/stickers and wash the bike to remove any oils.  Then scuff the existing paint with sandpaper all over to give the new paint somewhere to tooth into.
I would also strongly recommend you take lots of before photos and post them here, along with the serial number.  In the future someone might come along asking to identify their dirty old BMX that was overpainted decades ago.
Progress and post-painting photos might be cool too.
Do consider that this painting will void any and all warranty as well.