Even if siding does not contain asbestos, it could be in floor tiles and in other things. If you hired a company to do the demo and they find something with asbestos, they will have to halt the work until an asbestos abatement/removal plan is done and that will end up costing a fortune to get it removed. Best to deal with it yourself if you come across anything suspicious. Usually things with asbestos can be properly bagged and disposed of at the local dump. Check with local authorities.
You can hire casual help off CL as long as you contact your local workers compensation board and get coverage for any workers you hire. It's based on the payroll that you report. Never hire anyone or company to work on your property if they don't have workers comp. coverage. That applies to a company as well. Always phone and ask if their premiums are paid and up to date and have the required certificate/clearance letter.
I would go with doing the demo yourself. I torn down a really sh*tty 1000 sq. ft. 50s single story house on our property after building a new house on it. That was 8 years ago and got quotes of around $5K to get someone to come in and do it. I decided not to throw out that kind of cash and did the demo myself. Hardest part was the roof because of several layers of asphalt shingles and the thousands of shingle nails everywhere. Otherwise, swinging a sledge hammer around wasn't all that hard. Because I did the work by hand, I was able to stack all the lumber and plywood in the roll-off bins tightly. IIRC, I got it all in 2 bins. I started burning the wood at first until I got a complaint from a neighbor and that ended the burning. Would have taken another bin otherwise. I did get a few decent $$ from all the scrap copper wiring and pipe. The end cost of the demo was just the cost of the bins and they took all the stuff to a recycle place so didn't get whacked with high tipping fees at the dump.
Doing the demo myself wasn't all that difficult. I didn't have to deal with lath and plaster tho. I have in several other houses in the past and that is a nasty and dusty job. Wear a respirator.
I would consider salvaging lumber but only if you can de-nail it. That will be difficult if the wood is hard and/or nails are rusty. Lumber is likely full dimension. A mill will not plane old lumber if there is even a hint of a single nail in the wood. There is a demand for old lumber - it is likely first growth with tight grain and no knots. I restored an 1880s house once that had douglas fir siding and it was as good as the day it was sawn into siding. Just can't find that stuff anymore.
When I took the permit out for the new house, I had to post a $5K bond that I would tear down the old house once the new one was occupied. I didn't want to pay the cost of a demo permit (required here) and went ahead with the tear down. When it was about 1/2 demo'd, the township contacted me saying they wanted to investigate the house to see if it had heritage value and would have to be kept intact. They even sent someone out to take photos. You'd think they woulda checked this before insisting on a bond to to ensure I demo it... Ended up getting the bond back no problem.
Be careful as you reduce the structure to framing. You may need to add some temporary bracing.
You might consider a CL ad for people to come and remove items for salvage if they do the removal themselves. Just make sure you have workers comp. coverage or coverage in your homeowner's insur. policy in case of an injury (or worse).