I would do a bit of homework first . Call the longarm people in your area and find out how much of a back log they have. If they are all more than 3 months than ... your area could support another. Check out how much they are charging for services. Do the math .. how long will it take to pay for the machine .. how many quilts will it take to just break even?
Find out how close is the mechanical support you may need for your machine. Do you have dedicated space that can remain dedicated for at least 5 years.
Try to think about where will your customers come from , do they all have longarm professionals they are happy with? it is unlikely that once a good relationship is established they will switch. How will you break into your market? What will it take and what are the time and costs associated?
Can you handle the payments before it becomes a business? Like regular peice work long arm work takes skill and practice. One LA pro I know did over 80 quilts for charity before she felt she had the skills to truley go professional.
I guess it also comes down to is this going to be a dedicated business or a hobby that you sometimes make money. Manage your expectations first, by putting some numbers to paper.
I hate to say it but ... what is an exit strategy? In other words what if come to find out you do not like it .. ( for what ever reason) will you be stuck doing something you would rather not because of a payment on a machine. Find out what you would be able to sell the machine and how long it would take to sell. Ask the dealers for the machines if they have used machines and how long they have had that particular model ( and why it got turned in). I know a few LA pros that after a few years just burned out ... and only do a few quilts for close friends.
All that being said... Good luck , keep us posted