You have some great questions. I also need many answers for greenhouse growing. I had planned on posting a question, but had never got around to it.
My dh made my spring cold frame into an actual greenhouse. It does have dirt for the floor, but the rest is very solid. All out of scraps too. I'm so proud
. I only have tomatoes and basil growing right now, but I hope to get some herbs started next month. I have many huge plans but you can only fit so much in a 10 X 10. It is detached from the house. I doubt we would be able to attach one to the house, but I would love too.
My big problem with it is heat. We have black bricks, and red 5 gallon buckets filled with water. When it gets below freezing this is not enough. I've had to plug in an electric heater to keep it from freezing. I really didn't want to do that. I need to know how to keep the thing warm after the sun goes down.
I have the same dream as Chanley. We hope to have a grey water system in a few years. We use a lot of grey water in the summer. I just have a switch to make the washing machine rinse water go outside. No filters or anything.
The sink water would depend on what you normally put into your sink. Will you have a dishwasher with a seprate drain? If you do I would think you could just pipe it outside and have a screen on it. I wouldn't want to use any harsh chemicals.
To use a dryer vent you would have to have something to catch the lint that comes out of the hose. My dryer pipes into the laudry room and if I don't have the thing(sorry) the hose goes into filled with water it turns the laudry room into dirty mess. I don't think it would be enough to heat a green house, unless it was very small.
I have spent very little on gardening. I buy heirloom seeds and save them, I get cuttings from nieghbors and friends to start plants. I don't use any expensive chemicals on the plants and I compost household trash and barn litter.
You will need to answer all of the questions Chanley asked so you know what you need and want in a greenhouse.