Loading BSPs in DBP is very easy and I have had no problems with textures since patch 2. It also does light maps! One MAJOR downfall (that DBP can't help cuz I did something similar and found that out) is that DBP created lights don't light BSP walls.
The biggest advantage of creating your own editor is that it will be completely customized for your needs! I'd go with that route personally but it would run slower without good optimizations. Since BSP is made to partition rooms by visibility (specifically Z depth) they are VERY optimized for speed ever since the wonderful all time classic Doom (and maybe before)!
1.00 GHZ processor, 256 MB RAM, GeForce 3 64MB, SB Live!, 8 cans of soda per day