Is the concern the mulitple power adapters, USB connections, space or a combination of all three? Or are you thinking of removing the drives from the external enclosures and making them internal drives?
If it's power you'd first need to go round them and work out what each needs - noting voltage, current draw and connector type. Then try and find something that could supply all of them - but if there's a great deal of variation that could be tricky.
For the USB connections, a hub would probably do the job to combine them - but would ideally be a powered hub adding another power supply to the mix. Hubs with 10+ ports are available but will get quite pricey if you need USB3.
A case would depend on what they are and how much access you need to them. A PC case may not be the most appropriate option, though.
If you just want to take the drives out and stick them in your PC's case, then they are probably mostly, if not all, SATA drives inside the external enclosures, so you'd perhaps need an extra sata adapter for your PC, and bays to put them in.
