Sould I power up this feraligatr?

Why not? You should power him up...

Wynaut!?

I don't think Feralgatr is going to be that useful of a mon. I could be wrong. But if he isn't very practical then power him up or save the candy for more 2nd stage evolutions (for XP). I think there's a few mons out there that are just better at what he does.

Absolutely not. Way to much dust and candy involved. You can catch a Totodile with that cp and higher.

Moveset is not ideal, so I don't think it is worth the stardust. You could power it up to 900~1200 if you don't already have enough water pokemon in that range for prestige, but definitely don't max it out.