Is it wise to try and use destruction conjuration and illusion all at the same time?

It isn't a bad idea. Conjuration and Destruction go very well hand in hand, and Illusion can still be a great benefit, but it will cost a lot of perks to keep illusion spells effective.

3 perks trees to start is not bad. More than that I would say you'll be stretched too thin for a while.

I have 5 trees I want. One handed and heavy Armor

If you're using destruction magic definitely combine it with conjuration, it will go far at later levels.

You can usually combine a majority of the schools together for a good stand on combat. But those three, they will get your rather far.