"WineHQ sounds interesting, but do I need to dual-boot and have Photoshop installed in windows before it will work?"
wine can do alot but it is not a windows replacement for everything
if you must have photoshop, then a virtual machine is your best solution to avoid the dual boot, virtualbox is very popular
i personally dualboot all my machines, i use rarely windows so it is kind of wasted space on hard disk but it is there for those few occasions when is required
you can use gimp for a couple minutes, you will discover if it can replace photoshop or not in your machine
if it does, then you will like it alot because gimp works on linux, windows and mac
if i understand well, you say you want to assemble the last pc you will need, but you say you are young, 60 years old?
in this forum there is many users at their 80's so i think that this will not be your last pc