I'm having the same problem as Nobody1225 with skipping waves. I got nothing my first year (thankfully, because I mis-estimated the time it would take to dig out basic defenses) then went straight to lizardmen in year 2. Then, in year 3 I skipped goblins, elves, and humans straight to a single (small) wave of werewolves (thankfully most were killed by my marksdwarves) and more lizardmen later. I'm on year 4 now and I skipped ogres (and werewolves, if you don't count the one small wave) straight to treants.
I think the problem is you're using population and wealth progress triggers, both of which are kind of unreliable. The population usually explodes due to immigration (I had my cap of 100 dwarves by spring year 3) and artifacts can (and do) throw wealth off completely.
It might be better to use the trade triggers, as that will (usually) be a slower, gentler increase rather then spiking up in the first few years like the other two. Of course then the player can manipulate what attacks him, but considering you could just make a drawbridge door and ignore attacks completely if you want I don't think that's a huge problem. I have no idea what export requirements are for the different levels so you might export enough in the first caravan to trigger giants making this one too unreliable as well - who knows?
By the way I think treants are bugged - they are all laying down. I think you forgot to give them a nervous system which would be the same reason they drop all their equipment at the edge of the map. [NOTHOUGHT] should fix this if you don't want them to have a vulnerable brain to pierce. I have no idea what other side effects that token has (maybe none). This will probably also make them a bit faster (they are currently crawling around) so you should probably check they are still balanced. You also might want to give them [CANNOT_UNDEAD], though no bones and no skin might cover that.
Anyway the mod is a great idea and really adds a nice sense of progression that the game is lacking (at least until toady adds some next release). The variety of attackers keeps things fresh, and I *LOVE* the much lowered amount of junk loots.
Edit: Fixed redundant 'of course'
Edit2: I added [NOTHOUGHT] to treants and it fixed them crawling around - they are much faster and much more deadly. Also, building destroyer actually works on them (when they were crawling they didn't seem interested in smashing my things). They are more likely to get hit with bolts, but they are faster so they are in range for a MUCH shorter time and they shrug them off pretty well.