1996 Chevy Blazer 96 Blazer won't start without starter flu

Hello,
I have recently had codes for 2 oxygen sencors
which I replaced, also had a code for a small emissions leak. And one for a random misfire. My problem is that since I got this rig it has gotten increasingly hard to start, I thought it was related to the distributer, because while cranking it would intermitently fire I could se the tach jump when this would happen and then the next crank it would start
since it will run after spraying starter fluid I've been thanking maybe its the ignition module. I'd sure hate to ruin any sencors by using the starter fluid, and don't want to go compleatly dead in the water
any help would be greatly appreciated
Rob