I've run a 20-team league for several years and this isn't too bad at all. The pitching is a little weak, but there's plenty of time to address it. You're OK on closers (Rondon is a little iffy to me) but two closers puts you above the league average (also, with 20 teams that means some guys are going to have 1 closer and might be willing to punt on that stat after a couple of months so be on the look out for a good deal).
The key with 20-team league is that everyone is pretty much going to have a weakness somewhere and trades addressing position scarcity can really work in your favor (position is a Real Term in 20-team leagues, lol). That means that 2-for-1 and 3-for-1 trades are very viable in this format.
The other is being really diligent on the player pool/waiver wire guys. I guarantee you that at this moment there are 3-5 guys that are going to come out of nowhere in there and you just have to keep at it until you get the right guys.
My strategy in this format is to always go for the best player one trade at a time (with 2-for-1 and 3-for-1 trades) and just mine-mine-mine the player pool to try to recoup the lost value. It can be exhausting since it can really be finding a diamond in the rough, but by the end of the season you may be surprised by the roster you have (on occasion, my 20-team roster is better than my 12 and 14-team leagues, lol).
It should definitely be an experience, so have fun and good luck.