1. If you use the RAW files from a camera, then these have no colour space assigned until you import them into your image editor. Jpegs do have colour spaces, and all of my higher end cameras give my a choice of either sRGB or AdobeRGB for jpegs.
2. I always use a wide gamut workspace when editing; the only time I ever use sRGB is if someone gives me a file using that colour space. It's a one-way street; once you lose the colour data, there is no getting it back. Downsample an AdobeRGB image to sRGB, it will throw away some of the colour data and remap it to the best fit in the new colour space. Convert back to AdobeRGB, and those colours will not come back, but rather will be sample to the closest AdobeRGB colours.
Do I ever go back; yes, but only in very specific circumstances. For instance, if I am working on a composite in AdobeRGB and I want to incorporate a sRGB image, I'll convert to AdobeRGB, knowiing that I probably won't have all the colours from the original RAW file.
3. If you work sRGB, then there is no advantage in converting to AdobeRGB for printing; you may as well print sRGB. If you are planning to print in AdobeRGB, work in that colour space or a higher gamut one, never sRGB.