An average rubber dome keyboard is about 60-65g. Blacks actuate (i.e. the key is registered) at 60g. If you train yourself to only press them as far as is required to actuate them, then they are no more tiring than a rubber dome keyboard. If you press them down fully, the peak force is about 80g, and you'll tire your hands out big time. You'll probably find that if you move from rubber domes to Blacks, you'll spend some time mashing them down fully, but you'll probably learn to not press them too far just by continued regular use.
In terms of feel - given that they are linear, there's no tactile bump, but they are a lot smoother. While I prefer tactile switches myself, I have found Blacks to be pleasant enough to type on. Whether or not you'll prefer the Reds depends on how light of a switch you like. Reds have certain disadvantages - they're easier to accidentally press (although this is something that you get used to) and they're easy to bottom out on (again, something you can get used to, but may be a problem if you like pressing your keys with a lot of force), which can make them noisy and may potentially be tiring to your hands*. YMMV
* Note that these disadvantages are things I've observed from key switches that are light and/or easy to bottom out. I've not spent enough time on a Red-switch keyboard to confirm that they are exactly the same, but I have heard people who have say similar things.