There are a lot of questions which I don't have all the answers to, nor do I know all the questions. I'm sure others will post up with more questions to, not only ask the Contractor, but also ask yourself! Let's start with some questions you need to ask yourself, at some point, during the process.
Did I get at least 3 estimates IN WRITING? - does they include costs for demolition and disposal (if necessary), does it 'list' the mfgr. of the materials being used, does it give a start and end date? Did any of them side a house on my street or in my neighborhood? (Did I ask my neighbors/friends for references?) - if so, go talk to that 'neighbor'. There are plenty of nice days where you should see someone outside to 'bother' ... Do you need insulation board? - for example, if you have shingles for siding now, have them removed and 1/2" insulation board installed. He should, then, caulk any house gaps and tape the seams of the boards w/something like Tyvek Tape. Do you want any remaining 'wood surfaces', like window and door molding, capped w/aluminum? - This is a customary part of making the exterior of a home virtually maintenance-free. I suggest you price it, at least. Maybe you want only part of it capped. IF you decide to have part or all of the trim capped, have any rotted or bad 'wood' replaced. Then, clean and prime it before capping.
Questions for the Contractor:
What is the thickness of the siding? - Don't go any thinner than .042; it may 'droop' or sag in heat or over time. Can I see the warranty from the siding's mfgr.? - Read it yourself! Then, you need to insure he at least doesn't do the 'things' that the paperwork says will VOID the warranty. For exampl, most warranties say the siding needs to be installed over a SMOOTH, FLAT surface. I you DON'T have that, what's he gonna do to GIVE you that? Remember, he could VOID the warranty. Tell him you're 'concerned' if he doesn't follow it, and he needs to get a written waiver from the mfgr. if he doesn't. Also remember, next week, he may be OUT-OF-BUSINESS! Can I have WRITTEN PROOF of bonding and liability insurance and Workman's Comp.? - If you don't get them in writing, move on (at some point ...) Can you buy your own siding if you don't like what 'they' have for a selection? - Some siders limit their customer's choices. If you don't like what they offer, see if you, or they, can buy something else. Just try to go for something that's .042 or more in thickness.
You can save some $$$ by doing some prep work yourself. If you have 'old siding' that needs to be removed, consider that and get a separate price IN WRITING for that part of the job. Do understand, you may be responsible for disposing the 'old siding' yourself. That means a dumpster is necessary. (Only get it AFTER you are finished the demolition; not during it. You'll pay for a dumpster to sit there all week, doing nothing!) When they're about to put up the insulation board, run around with a caulking gun. Have some loose insulation too to 'stuff' in some possible cracks too. You can possibly replace, prime, and paint any wood trim before it's capped.
I wouldn't recommend doing the siding job yourself unless you have someone who knows what they're doing. Simply put, if you don't START the job the right way, from there on out, the finished job will look like crap. There are a lot of tricks to know and the DIY books are very good. But, the job is a bit intimidating. (I'm a DIY and it took a bit to get the hang of it. I had a friend who did doors, windows, and siding work for/with me to do this. I saved 50% on the job this way.) Others may have more to offer so stay tuned.
For now, my best to ya and hope this helps.
PS: If you have a deck that's in the way, talk to the sider about that. I removed a few boards on my deck so they could get all the way to the bottom, and I replaced them myself too. If you have any trees or bushes right up against the side of the house, consider removing or trimming them. And lastly, if you have a fence that goes right up against the house, talk to the sider about that too.