Have you checked the output from the CPS (Crankshaft Position Sensor) as these can fail suddenly and give simlar symptoms to those you desccribe.
Although i'm not a fan of using Easy Start for generally bad starting engines, it's a useful diagnostic tool here - spray some into the air intake while someone else turns the engine over, if the engine fires it's a fuel related problem. If it doesn't, look at the ignition, particularly the CPS to start with.
They can be changed (certainly on the V6 which is a similar engine except for an extra pair of cylinders at the back of the V8) in situ without a ramp, it's a fiddle and you need patience and cut-proof knuckles but it can be done.
Diagnosis is the thing here, a bit concerned about the key being left in the ignition when the battery was disconnected but that's probably due to the previous car i had. Also have you got a spare key? try that, see if it starts. 😉 😄