Is it a doomed to failure theory to panama an existing concrete yard 10' X20' to bring its increase even beside the foremost house slab? Or should the existing patio concrete be removed and pour new slab?

Or should the existing patio concrete be removed and pour new slab?
Is it okay to build a deck over...
if its only 3 or 4 in. , depart from it unless you need to accomodate a wheel stool...if its more than that to get to house height afterwards i would tear out and lay up blocks and pour a cap or build a deck to go and get to that height...
How to start a wormery/worm tend?
It is best to keep an outdoor slab okay below the house slab. In case of heavy flooding rain, you don't want to give the rain an opportunity for precipitation water to flood into your home.
I hide 2500 dollars contained by my house...
Bad idea -- the two layer won't "bind" together and as other answers mentioned having concrete above grade (especially above your footings or slab!) is asking for trouble when it rain. You'd be better off pouring a small step near the house.

Get a sledge hammer drill and drill 1/2"holes below where the step will be poured. "Dowel" the holes with rebar that will stick out ample to act as an anchor for the step. That eliminates the problem of the two layer not binding together.
Black Flies Everywhere :(?
Answers:    depends how much of a bonnet... a few inches would be a bad idea. the two layer will not stick together causing cracking and flaking, i would not recommend it. the proper way would be to remove the hoary and pour in the new.. of late make sure it is pitched away from the house
Finding the monthly costs for gas and electricity?
Like Harry said, it is a problem when your patio is even near patio door. You will have dampen come in.
I want minister to next to growing pineapples...
I am not an expert but I would be concerned about marine working its way into the house from the higher slab.