I feel like if you are going to run blastoise. You should go mono water. Having fire in that deck just weakens blastoises potential. You could have 3 energy in your hand if they were all water then you would be able to attach all 3 at one time + a plasma or DCE. However you could end up with 1 water 2 fire and some form of special energy and you could only put down 2 of them. Which imo basically loses the point of carrying blastoise in a deck since it takes 3 turns (without a rare candy) to bring it out and 3 slots for pokemon cards. Without some consistent way to search and bring out blastoise, i would suggest nothing less than 4-3-3 without rare candy or 4-1-4 with rare candy.
I'm going to assume you have something like 3-2-1 blastoise atm. With catchers easily bringing out squirtle/wartortle, and the sheer amount of other pokemon and cards in your deck, it will be tough to get it out consistently. Out of 60 cards you need 3 of 6 cards and at least 3 turns to build it up (assuming you get them in order). If you run 4-1-4 with 4 rare candy, 4 skyla, and 1 comp search. You need only 3 cards out of 18 cards in your deck of 60. Greatly increasing your chance to put together a blastoise. It basically makes like 1/3rd of your deck designed around pulling blastoise instead of 1/10th. It can increase even further if you include ultraballs, pokemon communications, and stuff of that sort.
But as you can see it takes up a lot of space to create consistency for one pokemon. Thus only allowing space for maybe one other line, 3-3 or 2-2. Of which it needs either be of use to your primary pokemon, or make use of your primary pokemon. Add in a few strong basics (i like to have around 9-12 basics total and maybe like 17ish total pokemon) for more consistent starts and you have yourself a pokemon set. At least in my theory.