Generally every pet can participate and get a few points. I remember my first war I still had my just-created-the-pet stats, plus maybe a few from Coltzan, and I got some
If you're wondering about your stats,
this is a good article to read about boosts. Right now your strength and defense are at the 20 boost, if you bump up your strength 3 more points you will be at the 35 boost (a good idea IMO). It is up to you if you want spend the money to train your defense 8pts up to the 35 boost also. I like HP, so if I were you I'd train that too. Movement and intelligence in general do not help you at all. Level's only importance is to be half your highest stat, or else you can't train any stat except it.
For abilities, get burrow (use earth faeries). (And sink (dark faeries), if you want to train to level 30)
I'm not a good battler really, but in general I think those are a few good things to keep in mind. I don't know much about weapons, my set is rubbish. Sorry!