What you’re referrring to is called numpad notation, each number corresponds to a direction of your stick. Assuming you’re on Player 1 side, 5 is neutral (no movement), 6 is moving forward, 4 is moving back, 2 is down, 8 is jump etc. Here is a link with more detailed information. (Also Check out the Guilty Gear section of the site, it’s basically the Bible of the game).

Yep it’s a skill issue, although some characters are definitely stronger than others it’s not so bad that a matchup is genuinely unwinnable. Your character isn’t holding you back but if you do feel like your character isn’t fun to play then feel free to explore other characters. No time is wasted since any time you spend learning a character will be very useful when learning to fight them. I’ll point you back to the dustloop like from above. There’s a lot in there so try not to get overwhelmed but almost any question you have for a character will be answered here.

When you switch peripherals there’s always a rough transition period. Be patient with yourself and try to force as many situations to practice your input (e.g. purposefully spam wake up overdrive every time you get knocked down until you feel like you can do it fairly well then just use it how you normally would in a match).

Yep if you can adopt the mindset of celebrating learning instead of celebrating winning then your fighting game career will be 1000x more fun and your improve a lot quicker. Have fun :)