I agree with the others about this being a very nice mod for the X. Typically I prefer no bumpers on these cars, but I do like this option a lot and have been considering it on one of mine for awhile. I realize doing body work is a major project, but ideally it would be nice to eliminate the exposed mounting holes and extra bits where the stock bumpers were. Same with the side marker recesses.
As for the bumpers finish. If you can, metalwork those welded seams to make them smooth and flush. Otherwise they will still show even when painted. If you go with painting them, the "chrome" paint option is very dependant on the product/technique you choose. In my personal opinion the chrome colored paints do not look good. But there is a chrome effect that is like painting, and looks really good. However it is not a DIY process as it requires some large expensive equipment to apply. But it is a lot less costly to have done than real chrome.
Another option might be to wet sand the existing chrome to give it a "brushed" look. This could hide the welded seam depending on how well they have been metalworked first. In this case I am not talking about using any fillers, but making the seams in the metal flush by welding and grinding them to a smooth finish. It takes multiple attempts with the welder, and multiple steps of finer and finer abrasives to get it nice, but the seams will disappear. Then the brushed finish blends them with the rest of the bumper.
Also you can "wrap" them. There are a lot of excellent finishes available in wrap materials. Including chrome, various brushed effects, various other metals effects (copper, aluminum, magnesium, etc), and much more. With a wrap you can use filler materials to help hide the welds first.
If you use regular paints to finish them, be sure to thoroughly scuff the existing chrome first, then use a good primer. Otherwise paint does not stick to chrome very well. I'd go with a black color of some type. But then I'd do the same process for all of the other chrome on the car so it is all consistent.
Nice work, car is looking excellent.