I lived on a slab for 19 years and never had bugs. Mice got in once by burrowing a hole through the slab, but we figured that out and plugged it and no more mice.
When I bought a large home with a basement I saw a lot more spiders and such. Had a fridge that was leaking (and I didn’t know it) and it never drew bugs and it leaked badly. Also had a commode in the basement bath that leaked and it never drew bugs.
Had a squirrel in the basement once that scared the heck out of me.
It sounds to me like the bug problem has been there for a while and the bugs are pretty well entrenched in the house and it’s going to take longer to get rid of them.
I know how frightening and intrusive a break in can be. But it does seem to happen to many of us at one time or another. Good deadbolts can make a huge difference and make sure you window locks are good ones. You can always get some pieces of wood cut to fit into the sashing of your windows so that the windows don’t open. Also if you have a sliding door, that might help there too. Get some of those timers for your lights, so the lights are on if you come home in the dark or leave in the dark. I used to leave the TV on when I left too, made it sound like someone was home. If you get packages, you might want to let the UPS or Fedex or USPS delivery person know to not leave them or to leave them out of sight so it doesn’t look like you aren’t home.
Make sure to keep curtains and shades closed at night and some days close them and some days leave them open when you are home so you confuse anyone looking at your house.
There are a lot of inexpensive things you can do to deter burglers and such.
Getting to know your neighbors can be a big help as well, then they will maybe help you keep an eye out for odd things going on at your house.
What was it about the house that made you decide to put a bid in on it, there must of been something you liked???