I would suggest, for the sand and street, a 1/10th 2wd stadium truck. the T4/XXX-T are great choices. stadium trucks have perhaps the largest selection of tires available. you can get street tires, or even paddles (for sand!). also, the 2 brands are usually supported by most hobbyshops.
also look at the new traxxas VXL rustler, it already has a brushless in it, and parts are widely available too.
I recently ran on galveston beach with a XXX (buggy), and had great success. i was running a Novak 7.5 Brushless setup, and 3800 lipo, and was getting about 20 minutes of runtime. Its fun to run in the sand, BUT you need to get SEALED ball bearings. i already had my buggy equiped with some (i think from BlueStarRacing or something like that), so i didnt have to worry about crunchy, siezing bearings.
as for a brushless setup, i would go Novak. why? because of its smoothness, and acceptance of various battery qualities. the MM (Mamba Max) tends to prefer Lipo or high quality Nimh. and MM tends to perform worse than novak when given small batteries (1500, 1700 Mah).
So, as a summary, i would get a T4/XXX-t, put SEALED bearings in, buy street tires/paddles, and equip it with a Novak system (7.5?)
that setup should be appropriate for your environment! i hope i helped! cheers.