It does sound as though your hive is in danger of SHB attack with the amounts of beetles you've seen. Eggs hatch within 1-6 days, so you might not notice the larvae in time. The larvae eat both honey and brood and leave a big mess. If your numbers are depleted due to splitting the hive, possible swarming and lack of brood, I'd suggest that maybe you should transfer the main hive frames to a nuc size so the frames are more protected. This will mean you can clean up the SHB as you go, too, so they have a fresh home. This is provided you have a spare nuc box. You would have to toss up whether it's safe to disturb them again so soon though with a possible new queen. One change the beeks round here made since the SHB visited is to keep honey frames off the unguarded wall, and keep the plain foundation there which the SHB don't touch. When the bees have the numbers to work on it they will be strong enough to protect it. Of course, I can't see your hive, so you know if it is a healthy looking size which you could leave alone.
You can find information about diatomaceous earth on the beemaster forum. You have to get the correct variety, which you probably would find out about at a bee gear supplier. There are thin traps you can get which slide in under the frames. You could make your own out of CD cases but I haven't tried this to make sure the SHB can't crawl out again to spread the diatomaceous earth around. You will never catch every beetle. I reckon putting a top cover on can be a haven for the beetle rather than a trap and the beek who had hives here has stopped putting anything on the frames except the traps. The SHB problem is not so great here I think because they can't pupate in rocks, but I have had a hive to the stage of having masses of grey goopy larvae before we realised SHB was in the area.
These are just suggestions..maybe a local there could help you inspect it.
By the way, have you thought about asking locals whether they would split hives for you as a way of building up numbers? If you have the nuc boxes then usually this is not too hard for an established beek.