Good growths really gives you the edge!

he got great strength, evades like crazy andif you manage to hit him, he got defense to the max plus over 60hp for being only level 1 (warrior class)!

I just finished chapter 10. I read in here that it wasn't really a good idea to advance your class at level 10 or something because of the skill thingy you get at level 15 so only Frederick and Kellam are advanced classes, really.
Buttttocks, my team typically consists offfff
Chrom (12 Lord)
Custom Character (11 Tactician)
Frederick (15 Great Knight, planning on making him a Wyvern Rider)
Sumia (10 Pegasus Knight)
Nowi (10 Manakete)
Ricken (9 Mage)
Miriel (8 Mage)
Kellam (11 General)
Cordelia (9 Pegasus Knight)

Though I guess this list changes a bit depending on how many characters I can use.

Looks like a pretty good list! Yeah I'd say go up to Level 15 at least, so you don't get screwed late-game and so you can get the skill.

Remember that you'll get much less XP if you're level 1 promoted than at Level 11 Unpromoted. The levels gained from 11-14 would probably be the same length as from 1-2, and you'll end up with around the same stats anyway.

It's simple math, really. You get a stat boost for changing classes, but that stat boost won't be all that different whether you go at level 11 or level 20, but in between, you have 10 levels of growth to get, then you can get the stat boost.

It's like if you auto-aged a 12 year old to age 18: sure they'd get the adult body, but the boosted 18 year old is going to be worse off than even, say, a 17 year old that aged normally, who's got five years of life experience on them.

I only recently found out that you go back to level 1 when you do the class changes, and that it gets harder to level.  However, something I really don't understand is what determines what stats go up when you level.  Is it just randomized?

Combination of the random-number-generator, weighted by the specific unit. You can tell what their general strengths and weaknesses are going to be by their class, of course, but each specific unit has unique growth rates, such that some may definitively be better units than the others of the same class.

Not sure about this game, but at least in previous ones it was a point all around for every stat (including build and movement) plus two or three in the "key" stats of that class, including those that are less likely to increase during a regular level up (so HP, Strength and Resistance for a Fighter, for example).

Each character was different, however, as was each class. So Chrom may level differently to Lucina, despite the fact they're the same class, because they have different growth rates.

That probably explains Nowi's occasional +2 HP for a level.

Ugh, I really want to try this out... but I don't want to dislike it. I'm afraid that'll happen.

First world problems. :P