Car batteries are made for a quick high amp discharge then a fast recharge, they are made with thin plates so they can do this.
They will last 5 to 7 years with that type of use.
A winch will need to draw steady high amps, this will shorten the life of a car battery, they are not made to provide long term power, they do not recover fully when discharged past a certain point.
Normal vehicle operation is, engine starts, battery is out of the circuit, alternator is powering everything, so the battery really isn't used that much, it only has 12.6 volts and vehicle runs at 13.6volts, so battery isn't used, this is why you can disconnect a battery after engine is running, although with the new electronics it isn't a good idea to test that any more, lol.
When you add a winch you should really add a second "deep cycle" battery, deep cycle batterys are made with thicker plates, they can't discharge full amps all at once because of this, but can discharge more than enough to run a winch, and they are made to be drained, that's the "deep cycle" part, drain and recharge, drain and recharge, drain and recharge.
Hybrid batteries(car/deep cycle) are not any good, they combine the worse aspects of both types, pass on them.
Any alternator will work if you have a second battery, but no alternator will work to power a winch AND the vehicle, so winch will drain the battery it is hooked to no matter what alternator you have.
Question is do you want it to shorten the life of your car battery or run a dual battery setup.
A second battery is just not used that much and if car battery is not being drain then after startup and recharge most of the alternators amps will go to the second battery and recharge it pretty fast.
So alternator size isn't all that important, unless you are running lots of light and other non-stock electrics, lol.
Second battery is good for that too, party all night with sound system blasting and lights blazing, no worries in the morning about starting engine.
Also, picture winching yourself out of a tight spot and almost at the top where you will be free.............engine stalls, guess what, it probably won't restart, the reason it stalled was because voltage dropped too low and electrics glitched, won't be enough amps left to turn engine over.
Winches heat up pretty fast and draw even more amps, best to run them for 30seconds to 1 minute then rest a few minutes this will give the alternator a chance to recharge battery as well.
If winch draws 400amps, then alternator would take about 8 to 10minutes to recharge battery, if winch was run for 1 minute.