Figure 8's can be tricky. Some people have good luck with them and they get along fine with the other fish and some people have trouble with them being aggressive. We wanted to go with them in our's but it's a 50/50 on the personality. It could very well work depending on how big of a tank, how many hiding places for the other fish and the puffers attitude. You can give it a shot and hopefully it goes well.
As for the way you want to go, that's all up to your personal tastes. Since all our other tanks are based on natural themes I had the idea of going with an oriental theme for our brackish. Since I wanted dragon gobys, I wanted something to pull it together and have balinese decor. You can see it in my albums.
Personally I'm not one for fake plants and bright gravels. With dragon gobys a sand or loose substrate is best since they like to burrow. We went with 3M black color quartz T grade, they also have S grade which is more sandlike. But as I said, it's really up to what you want to put in there and the desired effect.