Likely drugstore beetles. Too big to emerge from pinholes. Further, they don't eat wood (Ha! that's one of the few things they don't eat) They gather at windows because they "know" that light means the way out. Unfortunately, they don't know about windows which block the way out. Drugstore beetles may originate from a number of food sources, among them craft supplies (dry seeds, dry flowers, feather, and more); a seed stash in the wall (e.g. from mice, squirrels or other critters; leather; wool; drugs; and books. One of our office workers finally located the source for his beetles: the grain filled neck warmer that one heats briefly in the microwave.) Have a grain-filled pillow? So keep looking. Once you find the source, destroy it, then follow-up for any yet to emerge. Generally, tracing the origin of these beetles tend to be a person's new hobby, even if only for a while.

The above insect is not a beetle. Perhaps you should post an image of yours for a definite identification. If the insect you've observed IS a 14 spotted ladybug, then it's not eating your seedlings, but is after aphids and other pests. If the insect is actually munching on your plants, then you probably have a population of Harlequin Bug (but not a beetle), probably in various stages of development. The 14 spotted ladybug is not widely distributed in North America, yet. Where are you located? Let's ID BEFORE you worry about how to get rid of them. Here is a link that might be useful: 14 spotted ladybug

I'd need to see the back of the beetles (the top) in order to take a stab at identification.

I've seen photos of very elegant elm bonsai. I would never be able to do what was required to produce and maintain one, but I can still admire them. I would believe you can dwarf any elm with the proper techniques, but I'm sure some would be easier than others. I grew up seeing ulmus alata (winged elm) naturally bonsai'd by conditions and cattle in shallow soil pasturage in NW Arkansas. Typically they were as much as a foot in radius at the ground level, while only 3-4 feet high, and constantly pruned to a tight rounded umbrella shape by cattle grazing. They were very scenic, though somewhat larger than the average pot bonsai. Maybe topiary would be a better word? Fond memories!