I started out running portables. Nothing wrong with them, but after buying a truckmount I HATE using a portable (sometimes necessary when you can't reach an area with truckmount hoses, hoses cannot be run into an occupied building, etc..._).
I'm not knocking portable operators, but a truckmount does give you an "image advantage". Lotsa folks won't even hire you if you don't own a truckmount. Or, they won't hire you again. If I had to start all over again, I'd definately buy a truckmount to start out with. But, do some research. Some of the new, more popular TMs, will cost you upwards of 15K. Right now we're in a buyer's market for used carpet cleaning equipment. Look around on
Craigslist
http://www.truckmountdeals.com/
http://www.truckmountdepot.com/The-C4.html
and other places like carpet cleaning supply houses in your area. You can find some really decent equipment (truckmount AND van with tools included) for under 10K.
It's nice to start out with brand new equipment. But, not alway practical. The deals are out there. When/if you think you've found a good one, the guys on this board can help you make an educated decision. Heck, some of these guys may even find one FOR you if you are really serious about getting into this business.
It's a good idea to minimize your debt, but don't be afraid to take SMALL leaps of faith to obtain equipment that will make your work more efficient and less labor intensive. The first time you lug a portable up, and back down, 3 flights of stairs (like I did for several years) you'll understand. And that was back when I was in my 20s. NO WAY I would do that now that I'm 46.
VERY IMPORTANT:
Systemize your business.
Don't just answer the phone, book the job and go clean. You need systems in place NOW so that, if you ever do decide to implement employees, they will have clear-cut instructions on how to properly and consistantly complete the task.
But, even if you never hire employees, at the very least you'll be defining and refining your business systems that will make your job (and your life) Waaaayyy easier. And being a one-man-show (owner/operator), ALL the daily, tedious task will fall on your shoulders AFTER you've cleaned the carpets. You have to be your own secretary, marketing manager, accountant and team motivator. It's not as easy as it looks/sounds. It's tough to run your own business. It's even tougher to be consistant at it.
There's lots more to consider. Keep asking questions and you'll get the answers you're looking for. You're among some of the best in the industry here on this board. And there's very little the people here can't answer.
Good luck