If you're out with him then you'll soon spot any dangers or annoying things, find solutions then. Have a look round for random spots of cat poo, broken glass, old rusty nails, sharp garden canes etc.
Some kids are total wreckers and will pull up plants etc, others will mooch around looking, you'll have to wait and see what yours does!
Paddling pools you fill early in the morning on a hot day and they'll be warm from the sun by mid morning. It's not a bath though, they step in and out and that's part of the fun! You can also fill with cold and pour a couple of kettles of hot water in to take the edge off.
My kids have loved having old kitchen bits to play with, saucepans to bash, cups and bowls to pour water into and make potions in. A couple of cheap washing up bowls to play with are as good as any toys. We also have a bit of old plank we prop up to make car ramps on. Something like a scuttlebug or scooter to move around on is good too. You also need a bit of shade in the summer. We chuck a sheet over the rotary clothes dryer to make a tent.
DD has also loved having pots of hardy herbs that she can pick to smell or eat - mint, parsley, rocket, lemon balm etc. They're fairly unkillable.
With steps and wonky surfaces etc, they learn really quickly! It's good for them to learn how to assess risk for themselves and that it's not a good idea to throw yourself down a step etc.