Collect what catches your eye......
but take the time to educate yourself about the rudiments of bicycles.

Are you going to ride what you collect or are you more of a display your finds person?
Riders- in road bikes - come in a variety of sizes and geometries. Familiarize yourself with this aspect(fit) for
bicycles you will be riding.

While all bicycles have some things in common, there are huge differences in them.
Realize some parts are easy to find, others not so much.

Get to know the variety of threading(BSC, French and Italian) and dimensions(68mm vs 73mm in bottom brackets
and 1" vs 1 1/8" vs 1 1/4", straight or tapered in forks and headsets) and component families and their position in
the hierarchy of bicycles.

Brands names are a start. Proper names for the various parts and frame elements are important.

Bicycles can have hidden damage and issues(frozen seat posts and stems, cracks painted over and out of alignment frames).
Understand what normal wear vs excessive wear vs damage look like.

Spend some time (when it is possible to do so) in a local used bicycle store. Check you local used bicycle listings to acquaint
yourself with a wide variety of models(not sure if Craigslist is active where you are, but you can scan it for any major metro).

Some good books to begin your education. Glenn's Manual, Haynes Bicycle book for mechanics;
Sharps Treatise on Bicycle and Tricycles for theory on bicycles.
A Sutherland's Manual will provide a great deal of information on dimensions, mechanics and so much more.

One last thing, especially if you plan on doing mechanical stuff yourself- invest in proper, good to pro level tools.
Understand your limits to avoid creating issues. Wheels are an example - true, round and dish - just tightening a
single spoke can affect all three.

Ask a lot of questions.

Hope this helps.
rusty​​​​​​​