There have been several threads here regarding truck selection, fitment, design etc, etc. Some guys accomplish a lot with very little. Some guys have designed their rig from the ground up. It all depends on who you want to cater to. How much chassis do you need, how heavy do you objectively think you're going to be, then add at least 2-2 1/2 ton. Never know when you might have to cross a scale fully loaded with tools plus the machine component that's on your back heading to your shop. Then crane, how much stick do you need? Is it a manual pull out jib that you pin in place or going with a full power boom? Does it and your chassis have enough a$$ to handle your biggest job? Not just capacity but length. Can't tell how many times a guy goes to pick something and runs outta stick or capacity and it goes into HCL . When I was rolling my last rig, it was a stretched F550. Poor thing was 25,800 and I didn't even have all my tools on there. Company supplied, so that's the way the mop flops. If I carried fluids and filters for a 2k service, I was overweight. Be honest with yourself if you're going to be self sufficient or do you see farming out some heavy lifting. For example you could hire out a crane and operator for really big picks vs investing in "that much" crane. Weight is something you can't cheap out on, fines are steep and once yer marked, yet an easy target.
Good luck in your selection process