Go to a couple equipment shops. You and your friend do this together.
Talk to the guys behind the counter. You might not get to talk with the mechanics, but that is OK for now.
Talk to them about the equipment. Talk about the kinds of accounts you will be doing. Refer to size, guess at the amount of lawn area. Measure your own lawn and use that as reference. Discuss the option of used equipment, see what they have there.
Now while you are doing this, look around. Is it a shop that deals mostly with commercial clients? or mostly homeowner?
If they deal with commercial GREAT, your in the right place.
Get a feel for the guys there your talking with. Do you feel comfortable with what they say and their recommendations.
Go to another shop that deals with mostly commercial clients. Go through the same process.
Now the 2 of you decide what shop will get your business. Remember one thing. Who ever you chose, they will ultimately become your best resource.
Also many of the shops have a board where other LCO's post equipment they want to sell. Ask the guys at the shop about those as well. They should know the person selling them and might know of the equipment they are selling.
Anything else you need to know regarding the business. Just have a look through the threads in the forums that you are interested in.