heavy duty equipment can last a long time.
my advice is to not buy new, you never know if you will stay with this, or this is the career for you.
Why don't you start a computer repair business? It seems odd to make the jump into something you don't know or havent done?
A walk behind mower, used in a 48-36" deck size will be best.
You could find one new for around $3800.00
A honda 21" commercial mower will be $1000.00
A stihl PB 55 hand held blower will be around $200
A stihl FS 55 weed whacker should be $300
you can buy a neat little trailer at lowes for $2800
Rakes, hand tools, tarp, a 55 gal rubbermaid garbage pail say another $600.00
Misc stuff like gas cans etc etc figure another $250.00
thats all you will need to cut grass and do minor clean ups.
If you live in a heavy leaf state you will need more in the way of blower, but otherwise more blower is over kill.
That puts you in around the budget you were hoping to be in with good commercial equipment.
DO NOt buy a homeowner knock off of a commerical mower. You would be better off (WAY better off) buying a used commercial mower.
Don't look into a rider at first, unless you have massive lawns in your area (like Massachusetts/ connecticut region) even then start out small, find the neighborhoods with medium to small sized lawns that would can use your walk behinds in easily.