@ Edpon
Ooo, nice to hear about dates for MOS. Anyway, your questions (you'll get pretty much identical answers for OS4 as well)
1. Software: Yes, if it's system friendly. Old games need UAE. Disks will not work - there are no drivers for the Catweasel and the onboard floppy controller is a PC style one. If you make ADFs of your old disks you can use the images with something like diskimage.device, however.
2. Amiga feel: Absolutely. I switch between MOS and OS3.9 without having to switch operating mindsets like I do when switching between MOS and Linux. Taking the title out of consideration, you'll never know the difference.