Glad to see someone these days prepared to work to earn some money to buy what they need rather than relying on handouts from parents or other funding.
I think that sounds reasonable for a hand car wash, just make sure you do a top job - you'll probably need to get some decent materials to get started though and these can be expensive especially chamois leather if you use one. I remember doing something similar when I was younger and I think we did a rubbish job but we had regular customers so something was working...I remember me and a friend made 20+ quid in one day which 20 or so years ago was pretty good going!
Good luck with it. I would imagine there's nothing stopping you using a standard wireless card with the wanadoo service but I don't have it so can't be sure.