Winter is not the best time to be pouring concrete in Connecticut. Concrete setting up too fast will not be a problem in cold weather. You will be standing around at midnight waiting for it to get hard enough to finish. If you have to pour in cold weather, you or your contractor will probably need to use hot water in the mix instead of cold just so you can get done with the pour before the sun sets.

I don't recommend dumping bagged cement over your gravel, either. You don't want to fill the voids in the gravel; those voids between the individual rocks can accomodate a lot of water while it waits to soak into the ground.

If you were pouring a 4' x 4' pad outside your workshop door, I'd say go for it, do it yourself. If it looks like crap, you can always tear it out and try again. A pad the size your are talking about needs some experience and know-how, better left to the professionals.

Also, chain-link fencing would be a poor substitute for welded wire mesh/fabric reinforcement.