Dont go over 5 or maybe six if you know what your doing. Never try to have in all 8 types, anything from 2 to 4 works fine. IN my deck, i have water, fighting, metal, elecetrick and psychic, and it can get complicated when you use up all your multi/rainbow energies. 4 is enough, no more unless its vital. Five energies only works well when you can cover all your weaknesses, for example, fire, water electrick, fighting, grass. Water covers fire, electrick covers water, fighting cover electrick, grass covers fighting, and fire covers gras... ect.
Dont just play types that dont work well together in a five energy deck. Eg: fire, dark, psychich, elecktrick and metal. None of the weaknesses are coverd.(exept metal)
just because the theme decks have 2 types, doesn't mean good decks should.