It helps to keep the scale firmly in mind. If you've scanned your own textiles, you know what the dpi is; if not, you may have to work it out or take a guess. Either way, you need to know roughly how many dots per inch your textures are. Say you have a textile scanned at 100dpi. Then if you assume your figure is 36" around (again, it's approximate), your texture map should be 3600 pixels wide to begin with; the height should be whatever it takes to keep the aspect ratio the same. Unless you're wanting extreme detail, however, you would normally reduce your finished texture to something less memory hungry, say 1024 pixels maximum.