In your situation, you need to use LAN-to-LAN VPN, and one acts as Server while the other acts as client. The client-to-lan vpn is for remote access.

Yes, the R600VPN supports LAN-to-LAN IPsec VPN and client-to-LAN PPTP VPN.

The TL-SG105E supports one group of static LINK Aggregation, and it is pretty easy to do it, put the ports you want to aggregate to the group and then connect the ports. But you need to mind two...

Why not contact their supporter directly for help?

Hi, it is very strange I have to say. I am not sure what caused it, but we have a troubleshooting. Since the main difference between a dumb switch and TL-SG108E is that the TL-SG108E has a managed IP...

No, you need not configure anything like TRUNK or else, but you may mind the IP conflict. Since the default IP address of the router and the switch are both 192.168.0.1, you need to change one of it...