I just use Fit on the texturing and then change what i need to, it works quite well, but sometimes stuffs up.
Your tip 2 works well if you already have detailed textures, but i prefer to choose plain(er) textures and then add stuf. Eg, an imperial underground base on the engeneering level, now would they have pipes or electric cables? Both! and some wall and sceeling lights, and finally some support colums, great, that will do this section of the map, now what would they have on a corridor that vader could have walked down... It works quite well.
Another thing i have a problem with is fitting rooms and things into a bigger building, either there is not enough room, or too much. From the inside you think, this is too small, must make it bigger, and on the outside you think, this is too big, must make it smaller. And in reality they are rigth next to each other.