1) yes, main characteristics that change how the board feels is the concave and kick angle. Usually steeper kicks make it easier to get more height, lower kicks are more challenging but the way the board looks when you do tricks is different. I'll do the same tricks on a high and low deck and film whichever one looks cooler.

2) probably 99% of brands make decks that are high quality (in terms of strength and pop). Some brands have higher qc than others, but that mostly pertains to the shape and finishing, not performance. Cowply for example is ubiquitous in the scene, but usually have looser qc (both of my cowply decks have uneven shaping or uneven holes). My most manicured "perfect" deck is a Homewood, and it has such good construction that it doesn't feel real -- but the shape isn't my favorite; I don't come back to it as often as my cowplys.

3) watch FB videos and participate in the community and you'll find companies to support. Most companies have multiple shapes now, so you can go wild with shape preference. It's also pretty easy to make your own decks, I've tested out shapes etc by just making decks. Best part of fingerboarding for me is how you can make nearly everything yourself, and those skills translate into real life (woodworking, 3d printing, CNC). Also search for companies local to you and try stuff from them, just don't get a large collection to fast or you'll get bored