if you can, borrow the 450j. see if you can build a customer base. while doing this over the course of a year or so, log what other contractors have service/machine wise and see if you can develop a niche that no one else has. find a customer base than no else seems to care about and take care of those customers. purchase equipment than no one else has and exploit it to your full potential. look at what the rental houses have and see what they are overlooking.
for example, where I am from, everyone and their dog has a backhoe. so I don't own one because I cant justify it. In the past I hired others with backhoes to finish a job I couldn't do such as a septic system, or utilites tie in, and when I was younger and less experienced the backhoe owners would sometimes take my customers after completing the job that I hired them to do. that is a nasty feeling.
I recently purchased a Takeuchi mini ex just for the purpose of not having to deal with other contractors and the issues that arise from such arrangements.
I started my company in march 2002 with no experience other than being a farmhand. I purchased a used D4c and immediately had to start dumping money into it. 60 days later I broke my leg and was laid off at my job as a warehouse employee for walmart. it was very rough going at first, with no way to haul my equipment. My father helped me out and loaned me his 1979 chevy flat bed 1 ton pickup, and purchased me a 30 ft. gooseneck trailer on a credit card with zero interest. I was very thankful and proud to have the trailer and pickup. which leads me to my next point:
be sure you have a means of transporting your own equipment. I cannot stress how important that is. your competitors will not haul your equipment when you need it the most. it does not benefit them to do so. you cannot afford to rent a machine and then pay a delivery and pickup charge. it simply wont benefit your bottom line.
last but not least, being mechanically inclined will not hurt a bit. there will be times that you will have to spin a wrench or two, probably more than not. also have enough operating capital to finish a job.
when I landed my first dozer job, it was cleaning out a patch of stumps for a 20 acre show pen for cattle. I started this job on crutches, with no income for 90+ days, and when I fueled my dozer up I would back my 4wd lifted dodge up to the rear of the dozer and fill it with multiple 5 gallon jugs. was not fun on crutches. but I finished the job, and worked for the man clearing his land for many years afterwards. we became friends and I enjoyed working for him.
So, if you're gonna play this game you have to have a good attitude, and some good luck never hurt. looking back on it all I don't know how I made it, but i wouldn't change a thing and feel quite fortunate and blessed to be involved at the level I am now.