First...let me say i don't think you will be sorry if you buy this machine, especially what you plan to use it for. The machine was made to produce short run t-shirt transfers and decals. It does this very well...yes it is slow print/cut, but when producing 1-36, speed isn't going to make or break you.
Companies we have sold this to are just like you...wanting to produce short run jobs or just get into full color printing and expand their offering. I will say this...alot of times a call starts up with a bn-20 and then ends up being a 30" or even a 54" because of banners, wall graphics, yard signs, etc. You can do these types of applications on a BN-20, but it these types of applications, the size and speed don't make sense.
It is going to get a bad rap on a sign forum because of what most people here are doing...volume production on banners, decals, vehicle wraps, etc...all day every day. If they bought one of these machine, most likely they would not be happy.
So to sum it up in my opinion, the BN-20 would be a great machine for what you plan on doing with the machine.Is there a possibility that you can out grow the machine in a year...yes...but if you out grow it then it also served its purpose in making you some money to expand into even more. As far as ink set up...that is a tough one because once its set up thats how it stays. Me personally, i would go standard four color as the metallic and clear are beneficial in very niche markets.
BTW...we supply a complete stock of 20" media for heat transfers, decals, banner, canvas, glossy paper, etc.