In the 2 homes that we have owned, we have done it both ways. In our first home we had the oak strip flooring refinished and we painted the quarter round to match with the trim. In short order they were scuffed and chipped badly. In our second home we refinished the old oak strip flooring in the downstairs and they automatically stained the quarter round. I had never seen this before, but 30 years later, the quarter round is as good as the day they stained it. I love it. It does not appear odd at all. In fact it just blends in with the floor. We chose this staining again when we did the upstairs a few years ago. Upstairs we have some oak and some maple and both floors/quarter rounds look amazing, clean and unobtrusive.

This one is pretty easy. If you want grain, you must stain. Most stain companies don't really have a true black, it's simply just a super dark brown. If you paint, you may see some grain but it will mostly be incedental(thinner areas of the paint). If you paint, you will definately get a true color, but will lose the characteristics of the wood, because the paint is made for a higher 'build'or thickness to cover. Better quality paints and stains will not show brush marks, but if you choose to stain there are other methods of application like stain applicator pads(which I prefer) or others. You should always read the directions on the products however, as it will always provide you with the best application methods( you will usually see that it tells you to wipe off excess stain with a rag or tackcloth, hence removing the worry of brush marks!)Stain color can also be darkened with mulitple applications(coats). Maybe you may want to consider using both paint and stain. Perhaps painting the cabinets themselves and staining the top surface and/or drawers for a different effect. Just an idea...

Steam is not likely to be effective. You would need to heat the contaminated material to high temperature all the way through for an extended period. I don't know how you would do that to this structure. Note that I have no idea what "twin Ts" are.) The bleach will penetrate to a limited degree as well, but my guess it that it will work better than trying to steam it. I am still struggling with your description. Is there any way to post some pictures or do you have any links to similar structures? I am afraid that your best bet might be to just concentrate on humidity control to keep it in check after you make sure there is no water infiltration. Keep in mind that humid air that might be sucked in due to pressure differentials created by the HVAC can cause condensation wherever the hot, moist air first hits a cold surface. A few words on bleach. The concentration of hypochlorite is all over the place for some time now. It used to be a standard 6% by some convention. If you want to use the 5 or 10% figure, you need 6% hypochlorite in the bottle. The flavored varieties, as I like to call them, have a lower concentration so the added scents are not oxidized (degraded) by the bleach. Some shysters even market stuff as "ultra" that have lower concentrations than 6%. It is all a consumer rip-off. If you are in the store and forgot the 6% figure, check a bottle in the store that says "disinfectant bleach" on the label or has an EPA registration and buy the stuff that has the same or higher concentration that is least costly.

If you are keeping the stained oak elsewhere in the home I'd keep it there as well... If you are in the midwest, I'd lean toward keeping it for that reason as well. Personally, I think that painting all of the wood would look more updated and modern, but I'm in the minority in my area.