A pH of 7.0 is high for optimal growth of azaleas and rhododendrons. Your proposed solution of using raised beds is an excellent idea. To answer your specific questions:

Winter hardiness should not be an issue. Rhododendrons and azaleas are shallow rooted anyway, and a raised bed will not make a difference.

I would recommend avoiding so-called topsoil entirely. It's often of low quality and is too fine and easily compacted to promote good growth for azaleas. The best planting medium in my experience is partially decomposed conifer bark. If it's available locally pre-mixed with compost, so much the better. Bark with or without the compost is a naturally acid medium which is not overly expensive and will provide good water retention along with lots of air space because of its coarse composition. No exhausting mixing, either.

Some people advocate putting down a layer of heavy duty landscape fabric at the bottom of the bed to prevent earthworms mixing the underlying neutral soil with the acid medium, but as long as the mulch is renewed periodically it's probably not necessary.

You'll need a depth of 8 to 10" and something to outline the bed. Stone will last forever, but may be expensive. Logs are an option as are landscape timbers in a more formal arrangement.

No reason why you can't continue growing azaleas - good luck!