This was my experience, not exactly the same, but similar: Had some wood in a bathroom that I wanted to color, but also wanted to keep the 'wood' character - the grain, knots, etc. On the advice of someone that did a lot of painting, I picked out a color that I liked and diluted the paint by 1/2 with water. Painted it on, and loved it. Just what I wanted. Why don't you try this with a sample piece of wood? Now, about the turning colors - I never noticed it. Of course, the wood in that house was already about 50 years old, and I did move out of the house a few years later, but I would not worry about this. If anything, the knots may get darker, but I think this would just add more to the character that you want. I say - go for it. I think it's a lovely idea and will be beautiful. :)

I white-washed my red bricks about 25 years ago. Easy and I think it looks great. Still did when we moved out 4 years ago. I don't recall having to wipe anything off. I did most of it just during my kid's afternoon nap time. And my brick was about 6 feet wide, floor to ceiling, 9.5' ceilings. I just thinned white paint with water, sponged it on, and had plastic on my wood floors with towels layered on top to catch any run-off. If I recall correctly, there was a little but not much. The plastic without towels probably would have worked fine. I worked from top to bottom so I was able to quickly sponge any lines of paint that did stream down the brick. I'd say give it a try. If you don't like it but were going to paint the brick anyway, you can always paint over it. Personally, I hate the look of painted brick so I was a bit worried but hated the cheap brick (really Z-brick facing bricks) in my 1908 house with all the original, unpainted woodworking. It was a modernization attempt gone wrong. Might have worked better in a different style house. What I really liked about it is that the brick looked like real white brick when I was done, not like bricks that were painted. The paint was thinner in some areas than others so a little bit of the brick barely showed through but just looked like darker spots, not like red brick. It looked very natural. I received many compliments on it. Give it a try. You really have nothing to lose if you don't like your current brick.

If you are redoing the floor, I think the time to take out the half-wall is now. If you do it later, you will have to patch the floor. Does it separate the entryway from the living area? I like having some separation, but if it were me I might replace the brick planter with a framed half wall. No more brick and no reminder that people in the 70s thought that permanent built-in planters were a good idea. I'd want some contrast between the wall and the brick, but I don't have enough personal experience with whitewashing to know whether you can get that using the wall color on the brick.

Your fireplace looks nice to me, but if you want a different color, look into Romabio lime wash.