As your sockets are just replacement, that's probably about right. At least you havent got to lift floors, run new cables, etc.
I would up your per downlight price by a tenner each. there's a lot of messing about with those, especially if you are on your own.
Beware of assuming wall lights will be an easy swop. they aren't. (Hobby horse time).
The MD of companies making wall lights should be COMPELLED to try and install one of their lights. Often they are only just able to accomodate one single cable in the housing and supply a stupidly small terminal box to do this. Often you'll have two or more cables to deal with.
Then you'll find that the supporting brackets can't go where you want them to go because theres a great big hole from the old wall light, or because the cable runs just where the support screws are to go.... its fun (not).
Those plaster fittings are a challenge too. You'll need a cranked right angled screwdriver to get to the screw head.
I'd add at least half an hour to your assumed time for each light.
Materials price. Even for mates I add 20% to my cost. More for everybody else. He may be a nice man, but you have a living to make.
If you buy materials you have to add your time to identify the products, order, collect or take delivery. That's all your value add and your time. And then you will take on the responsibility for the materials.