1)

NAT

I try to forward my VPN (Port 1194) from outside to my synology as VPN server.

This setup does t work and I can t find any logfiles etc. to see what happens. No chance to see if forwarding from the fritzbox is working.

Using a Astaro/ Sohos UTM as internal router worked fine vor years.

 

Have you set the NAT forwarding rules on both the Fritzbox and the TL-R605?  Sounds like a double NAT setup.  As the fritzbox is a router set it to forward port 1194 to the tl-r605, then set the tl-r605 to forward 1194 to your synology. 

 

2)

Trying to save a VPN config ends with a jason error. A known problem?

 

Not that i am aware of, post a screenie if you can.   Are you running firmware 1.0.1?

 

 

3)

Is there a central function to manage all firmware-installations of all devices?

 

Firmware is vendor specific and there is no software that will do all your different vendor devices, however if you are referring to Omada range specifically, this is done via the controller (OC200 or Software).   It can centrally manage your setup and report/update firmware as expected, however this is only on Omada SDN capable devices. 

 

As said, sadly no one solution for all if that is what you meant.