I believe that angioplasty has come a long way in the last 15 years and what was considered ridiculously risky back then has become more acceptable. However, there are obviously still some restrictions such as location and size of the occlusion.
With regards to your vein grafts, I was told in 2007 by a surgeon that they are expected to last over 20 years now. Mine lasted three months but nobody can tell me why.
You are correct in that you can have your mammary ateries used, the Lima/Rima. Being arteries these do last longer than veins, mine is still open while the veins have decided to go to sleep. With regards to stenosis, it depends on the restriction being caused. If you 30 occlusions of 40% then you should be fine (in theory). Only 70% and above is considered a real problem. So, although you may have several other stenoses it may not be as dire as it sounds.