Replying to Landscapeing help needed!

i currently am 17 and have my own lawn business which i have run for the past 4 year its going well considering i work at a wage of $30 a hour and only work 12 hours a week. (last year) In last year i made about $6000 and i enjoy it cause its great money, last mower i had was a 22 inch briggs and stratton which i ran to the ground with over 300 hours of work in 1 summer. ( i found the mower in the trash with a ruptured gas tank and had to fixed to new by a mechanic) im hopeing to expand my buisness and purchase a new mower this year or used. now then i am going to college in 2 summers, so the mower will have to able to be handled by my sister or an apprentice during the months of april-may and sept-nov well i am at school. i want a 36in walk behind because its small and offers manueverablitiy in the small 1/2 acre lawns i do. i need some opinions on what to buy, want to get cheap around 700 willing to dip to 1000. please comment and help me alot so i can progress.

side notes
7-10 lawns per week last year
25-30 dollars a lawn
apprentice will be about 13
looking for around 36 not much bigger cause for now i will be walking to jobs, or riding if i get a deck to stand on
walk behind prefered definately
hints on a good weed wacker?
Thanks
Tyler
Means Mowing