Good plan. If its a NE forecast on any weekend, get out of bed and get in the car. Even if it's less than 2 knots all day at Manly (which is usually is anyway), it will still blow 99.99% of the time at Gerroa.

To answer your questions....

1. Either one. Or just stay in your car if its only for one night.
2. Yes, but is easiest from the 7-Mile beach one in the section on the beach side of the road.
3. About 2 hours
4. Warilla Beach (south side of Windang Island). But you may as well go to Gerroa if you bother making the trek. If there's surf, there's no better option. Warilla is a great option if there is no surf at Gerroa. Or just go down the beach from Gerroa to Shoalhaven Heads. Always a wave, wind just as strong (if not stronger), but cross-onhore direction.

Bring on summer!

Love Gerroa, had some great sessions there last season :D

Couple of extra things I reckon are worth a mention.

If it's windy in Wollongong (Bellambi AWS) it's most likely nuclear at Gerroa/SHaven. It's almost always at least 5kts stronger down there (more like 10) due to the local geography etc.

I also check the Shoalhaven surfcam on costalwatch http://www.coastalwatch.com/contents/default2.aspx if there are whitecaps you know the trip won't be wasted.

Lastly, from my experience Gerroa is at it's best when a S-SE swell is running. Even Easterly swells have trouble getting around the heads (different down at SHaven) and NE swells have pretty much no chance. So when swells of that direction are running it's usually pretty small, can still be great fun though. You can always go try out the massive rip/ramps at Shoalhaven :)