Although I hate to do it, (I'm a nature take it's course kinda girl) I have found that the predatory wasps in my area are so rampant that I had to screen my last batch in. But yes, if you are growing them in an enclosure already, just placing them on their food source and making sure there is enough of it should do well. Others with more experience will surely give their notes as well :)

What kind of wood is it? Solid or engineered? You could have them cut out those pieces and redo? The baseboard would have to come off as well but it is really not a big deal to fix if it really bothers you. The last board in the room has to have the protruding groove cut off so the last board is slipped in place and then face nailed. You could have them redo if you have extra board but like the above response explains...wood does shrink and swell so you may want to see how it looks in the summer before deciding to fix. I don't even see any face nails in your photo so maybe that accounts for the wobble which is not normal. Maybe they forgot to nail it in from above altogether? I have a few boards that I didn't have the guys face nail in so I could rip out the tile next to it and those don't move at all even without nails.

Please have it inspected and in my opinion, every home buyer should insist on this before purchasing. We had our fireplace swept after having neglected it for a few years (not very many fires in that time) and it was unsafe! At the top some grout (whatever you call it) was out and exposed a piece of wood (shouldn't have been that close to flue)! A fire hazard, for certain. My next door neighbor was concerned and had their fireplace inspected and their problem was worse than ours! For the safety of your family, please don't assume that any fireplace is safe to use.

Based on what you described: Do not apply anything unless you know what the problem is. (Btw, where does vegetable oil idea comes from? Just wondering - didn't come across that recommendation yet) Chilly windowpane is no problem - unless leaves/part of plant is touching the glass, and there is frost on it. Or really drafty... In z5, I have them on windowsill a do not worry about chill.. Cooler temps during nighttime are often quite suitable for many plants. Watering 1x/week is probably too often, and even more so if the potting soil doesn't drain fast. I can see some perlite, but can't tell what is the mix made off - do you know? How warm is it in the room they are kept? As for the white spots, are they web-like? If so, it may be mealy bugs. But I really can't see detail well enough to be sure. Does it look/feel papery-like? The larger cacti may have rot problem - I never had to do surgery on something similar, so hope someone else will post with good tips. As for light, they need as much as possible - many of us use lots of supplemental lighting during dark & short days of winter. It is a good idea to isolate new or diseased plants from the rest, usually until there is no sign of disease/bugs anymore.