I have an older chuck n duck drum chipper with the ford straight six. I bought her off of e-bay for 3600. I had some alternator issues but she is rock solid and handles all the brush great. If it is over 4" I use it for firewood, except pine. That being said make sure you replace the belts, oil, filter, plugs, plug wires, etc before you put it into full time tree work. On Friday ( the 13th of course) she ripped the main belt, the breather overfed the engine and the resulting backfire blew the muffler apart. As far as considerations for your business, look at your budget, planned growth, abilities to do maintenance/repairs or pay for them, and your equipment vs. manpower workload. Do your research, hydraulic vs manual feed, options, gas vs diesel, disc vs drum, the predominant type of tree work you will be doing, etc. etc.