Your purchasing questions depend on where you live. If you live in the US you can get a small terrarium and the shagum peat moss from this site, look at the accessories section.
If you are in the UK, homebase sells peat moss (only place I could find it) and a lot of people use aquariums and terrariums bought off the internet. You could probably get them from DIY shops, garden centres etc. as well.
Leave the traps with the beetles in and it will take a couple of weeks for the traps to re-open as beetles are hard for them to digest. Then when they re-open don't feed the traps again for a while (a plant doesn't need to be fed at all, but in the future one or two medium sized flies per PLANT per month is fine).
As for the fertlizer soil mix, you can rinse the current soil through with distilled water (pour water from the top (not onto the traps though, just the soil), and leave the plant and soil (still in its pot) to completely soak in distilled water for a few hours and then let the water drain away). You could repeat the process if a lot of fertiliser was added.
If you think the soil the VFT is in is completely wrong, repot it into a new soil mix. Peat moss: perlite : sand ratio of 2:1:1 or something similar. And still do the rinsing mentioned above to rid the roots of any fertiliser. A 3-5" pot should be a good size to repot into (depending on the size of the VFT).
If you are going to repot do it as soon as possible, so that the VFT still has some of the summer left to grow and get back from being repotted.
Hope this helps