To question 1, more or less, no. In a way it potentially could if a player earns a skill point and gets a bump in OVR it could push them above another player with the same OVR but that's a rarity and regardless of preseason performance, the depth chart will sort by OVR.
To question 2, you earn XP to get skill points. You earn XP from things like practice, weekly and season goals, awards and more. Skill points upgrade any archetype 1 OVR and when using a skill point you'll get attribute upgrades specific to that archetype. If you look at the player card for any player, you'll see their XP progression towards their next skill point in the bar under their OVR in the top right:
Also if you toggle to the right and go to progression history, you'll be able to see exactly where your XP is coming from as well as any changes to the players confidence. And the reason you got some skill points after one preseason game is because when you start a CFM, players will start at any range of XP from their next skill point.
Hope that helps!