1st read EVERYTHING here: https://www.sheldonbrown.com/

2. $1000- will barely cover tools, if you don't have any. I have been acquiring tools for 50+ years to be used for various projects, and from time to time still spend another $100- or two on bike tools.

3. Building a bike will not teach you all about how the components work and interact with each other. A bicycle is a relatively simple mechanism, which can be described with high school mathematics.

4. Before you start, write down a list of what you expect from the bike: where are you going to ride it, terrain (hills, etc), what are you going to carry on it, what are you going to use it for. My latest project is a commuter bike to take on Caltrains. I checked into the restrictions that Caltrains publishes. I hate riding with a backpack. It has be easy to take up the 5 stairs into the gallery cars. Be rugged to withstand the stacking of the bikes on the trains, the up/dn stairs in a rush. And many other requirements. I have two commuters that I use on Caltrains - one is built from a mid '90s Trek 720 frame I picked up off Craigslist for $25-, the other is built from a '92/'93 Trek 750 Metro that was also a C-L find. One has butterfly bars, the other Oxford style. One has V-brakes, the other cantis. One is a 3x8 with friction shift and the other a 1x9 with a gripshift. And lots of other differences. They both do the job well.