New machine purchase advice

I don't know if this is the correct forum, but here goes. I need a new PC. I set up in rather dusty environments for up to a month at a time. I like ~15 inch towers so I can open them, blow out the accumulated dust, or add any gewgaws that happen to appeal to me. I am not a gamer, but I do like streaming audio whilst working.
I do not know whether I should go with Win7 pro or Win8 pro. I understand that Win7 support will probably expire in 2020. I do not intend to expire in 2020, so I want something I can continue to use. Should I hope that MS will have a new OS by then that I can up-grade to.
I will set up Windows Virtual PC so I can run some older software, and will probably add another HD and perhaps video and sound cards later. Should I go with i5 or i7 CPU? I do run some mapping programs, and other assorted software needed for oil exploration. Mapping programs, particularly, can be CPU intensive.
I like the idea of having a recovery disk, rather than a recovery partition on the HD. Do I need one?
I know this is a long winded question, but please recognise that I suffer from TDA (Transient Dumb Ass). Thankfully, it has not progressed to the chronic stage yet. Thanks for any advice you can give me.
oldjeff