How wide and deep is your toekick area that you are trying to fill? IMHO, simpler is better. Rather than cut blocks to space every foot or so, why not just use a solid piece of lumber across the whole thing? Say your cavity is 4" high by 3" deep, and your baseboards are 3/4" thick. You could take a 4x4 (which is 3.5x3.5) and rip it to 3" (cavity depth) - 3/4" (baseboard thickness) = 2.25" thick. (If ripping a 4x4 is not possible with your tools, you could screw a 1x4 to a 2x4 for the same effect.) It does not matter that this is not the same height as the toekick cavity. Then you will have the problem of attaching this fairly thick board to a flimsy toekick, without backside access. I would predrill and countersink holes in it for construction screws in it, and screw it to the toekick. Now you have a sturdy substrate to nail your baseboard to. After attaching the 3/4 baseboard, it will be flush with the cabs. The hefty piece of lumber seems like overkill, and, frankly, it is, but it is easier than cutting and fitting individual blocks.

Given my choice, I do all my prep in a room first, then paint ceiling, then woodwork, and then paint the walls last. Is much easier to get a razor sharp line at the baseboard to have all caulking and painting of the baseboard done before painting the walls. I blue tape the baseboards using the low tack 3M tape. However, this procedure requires that the walls be painted the following day. Sometimes you don't have the luxury of time. If possible, I prefer to do all painting before new carpeting goes down. I prefer to work after new hardwood floors installation, taking the trouble to completely protect it with rosin paper.

It’s a distressed floor and isn’t a smooth flat surface so I expect there will be gaps. Nothing is perfect but I prefer no shoe. I read the pros and cons of a micro thin caulk and have talked to others who say it’s a good alternative.

I like the molding in the picture because its modern so it goes well so if you want a more traditional look then yes more detail would help with that otherwise I think the simple square ones are good and actually probably easier to clean. I hate shoe molding and in my own home had them put this little flat rectangular molding like a mini version of the the molding in the picture and it looks good and is thick enough to work as a shoe mold