Newbie Needing Advice

Hello guys

I had a fish pond that was 24ft wide by 17ft depth with 2 feet steel beam supported walls ... it was built like 60 years ago .. i removed the walls using a kango and i took it down to its base level and all that i had left was the pond slab of concrete.. i built walls all around to the height i wanted and infilled it all with what i earlier removed and used this as a hardcore base.. i have spreaded sharp sand on top to level it all off. my aim is to create a patio area and a place to house a 16x12 shed . what i need to know is this

1. Is what i've done suitable enough.
2. can i just lay the slabs on top and will this be sufficient as a patio area
3. can i just dry lay the slabs or do i need to hold them down with concrete dob&dab to hold them down.
4. Will this be suitable enough for the shed to be placed on.

Please forgive my severe lack of knowledge lol.