It tells you the base stats when you a summoning the primes. TBH though, chances are you wont have enough troops to fill your primes for some time. If you have too many troops for your primes to carry, go attack something so you can get Prime and rider EXP. Once you get into the second tier of primes you will have lots of room for your troops. Plus you need to leave some of your troops on your islands to help defend it.
Side note to new players: don’t waste time with your fighter prime. as soon as he reaches level 5, kill it and summon one or two of the better primes.