The problem with brazing stainless is that it has a narrow temperature window in which it can be brazed. If you exceed that range the surface will be corrupted and not allow silver to flow. Fixing the problem would require taking the assembly apart, cleaning it again and doing it over again. In most cases that is impossible and the frame in reality is destroyed. In addition it requires more strict cleaning before assembly and stainless steel doesn’t transfer heat as well as regular steel so your heat pattern has to be more precise. Regular steel is much more forgiving. In addition you don’t want to be using light heat treated tubing for a 1st frame because it can not be aligned easily. Frames go out of alignment because a beginner is not able to heat a joint evenly (or know how to start with it aligned). In my frame building classes I want my students to have a good experience and that begins by not putting them in a position where they are over their head and get frustrated. It only makes sense to start with projects that can be done successfully and as skills are obtained then one can go on to the more difficult projects. Doing bad on good stuff is a real motivation killer.
I don’t like to sound like a father of a pretty daughter warning a potential suitor what will happen to them if they don’t do as I say. However many years of teaching others frame building has taught me that almost everyone needs proper instruction to make a decent frame starting out. The vast majority need constant supervision or they quickly go off the rails. It is a rare person that doesn’t. There is a huge advantage to starting right and not having poorly made frames around that might last much longer than you might wish when you finally improve. If you should decide that you want to do it all yourself it only makes sense to use heavier non-heat treated tubing (like True Temper’s RC2 series).