I was a newbie not so long ago, and found myself in very similar circumstances. I don't know if you already know this, but:
~ "Speed" is a shorthand way of communicating how fast the disc should be traveling in order to behave as designed. In other words, if you can't throw it fast enough, none of the other numbers really matter
~ "Speed" is related to measurements of the disc itself, inclduing rim width and depth. I hoenstly believe it's a "best guess" applied by each manufacturer - there is no exact science
~ Flight numbers might be accurate to gauge performance within a manufactuer's offerings (a 9 speed disc needs more power than a 7 speed disc made by the same company), but they vary tremendously from company to company (you'll find that comoany X's fairway driver is much more stable than comapny Y's even though they have similar numbers)
~ Do NOT fall for the "great disc for every type of player" hype. It's simply not true, and some manufacturers are pretty egregious with these claims in their marketing
~ Learn to throw putters and mids flat and straight. Look for telltale differences in their flights (like more fade at the end, and hints of turn during the flight). You start seeing that, and you're ready to move up.
~ Have fun, and think twice before you buy anything based on what you read on the Internet. There are lots and lots of great discs to buy, and some fit your game better than others. It takes trial and error, but it's way too easy to end up with boxes of barely-thrown discs that just turn hard left and die (not that I would have any personal expereince there…)
~ Play with friends and others at the course. Watch what they do and ask about their discs.
~ Enjoy, enjoy, enjoy.