We will be visiting the Brac later this year...
do you have to go through customs in GC and collect your bags and then go back through the security to catch the flight to Brac?
yes.
How is the flight on the otter aircraft? never been on a prop plane before so I'm wondering about the flight.
its not bad if you get a seat inside the cabin. Its tougher when you're on standby and they bungee cord you under a wing, especially on rainy days. FYI, do expect that only the tiniest of carry-on bags will go inside the cabin - most will be gate checked. Also be VERY aware of their weight restriction rules for checked baggage .. they made me pull out ~3 lbs that I was overweight on a 50lb bag (and "hide" it in my carry-on...go figure). Also be aware that GCM's security checkpoint is horribly overcrowded - - pay attention to the size of the line and leave yourself extra-extra time to get through security into the waiting lounge.
is there a map available for shore diving? best dive sites?
Here's my old one, with descriptions (a bit dated). In general, you'll find people will recommend Radar & Buccaneer...these are old sites that are well known. FYI, its also a reasonably good idea to dive with a dive flag, since officially they're required.
FYI, I have a newer 'Total Island Map'
on Google Maps here .. it covers restaurants, markets, etc too.
Not really that much. I believe that the current status of the Alexander hotel is that Dilbert might have shut it back down again (money+politics); if its open, the restaurant there is one of the best on the island. There's also Captain's Table and the bar at Brac Reef as what's on our short list...for local (pedantic: Jamaican) food, I'd check to see if Aunt Sha's is open & running...things changed there last year.
We are renting a condo with kitchen so where is the grocery store?
There's three (3) major ones and during your stay, you'll probably get to all three, as what they stock (and don't stock) varies:
Marketplace - at Tibbet's Square (north side, cross-island road near the airport)
Billy's - north side, around a mile east of Tibbet's Square (2 miles west of Stake Bay)
Kirkconnell's - north side, Stake Bay
Personally, I put Billy's & Marketplace above Kirkconnell's. Don't be too surprised at the slim pickings in comparison to USA markets...for example, I think the only place we've found Greek style Yogurt is at Marketplace. FYI, the supply ship usually arrives on IIRC Wednesdays, so fresher stuff will be stocked on Thursdays.
Finally, be aware that liquor stores are closed on Sundays. Similarly, a lot of stuff doesn't have late night hours.
Hope this helps,
-hh