www.cgtextures.com
that is usually where i go for some quick base textures. they’re free, but you need to register and you also have a limit on how much per day u can download (its by IP adress i believe, so making multiple accounts doesnt change it…suggested to save everything u grab from there)
if you feel like buying textures (recommended for some cases), check out www.3dtotal.com. in their shop they have a series called total textures… really amazing stuff.
as far as your sculpt goes… i was in the same boat yesterday… trying to get responses, being a beginner myself. what was suggested to me which helped TREMENDOUSLY! was go get some muscle anatomy references (preferably one that names the muscles on it), and just go in and start sculpting out the shape of the muscles with the clay tubes brush (and alpha 06 seems to work best with it). but dont do that at your highest subdivision level.
start from level 1, and just brush out the shapes of the muscle. you wont notice any change but the program will pick up what you are doing. after subd 1 move to 2… and repeat. i did this all the way to subd level 5. afterwards you can take the smooth brush on a low intensity and just start smoothing out the peaks and valleys.
also… when you get your shape down… check it with a flat shader, so you can tell how your silouhette looks. you dont want to start sculpting immense ammounts of detail on a badly shaped model.