Suggestions with my mono green deck mtg?

I would add Llanowar Elves, and also look into some better six drops if you have the money to spend. Against U/B Mill you should be okay if they are relying on archive traps since you just need to not search your library. Just make sure you can get enough on the board to beat him before he starts milling you out. Aggro has always been a mill deck's downfall so if you really want to beat a mill deck just turn this into Elves. The only really expensive card is Vengevine, but you can get away without it for now.