I would recommend you look at this raspberrypi.stackexchange question.
Very breifly, you need to setup routing on your Rpi using iptables to route the VPN traffic that it receives from your remote client to your local LAN.
You should assign fixed IPs to the clients. E.g. ccd/client1 might contain:
ifconfig-push 10.8.0.112 255.255.255.0
push "route 10.10.0.112"
This way the client receives a fixed address (10.8.0.112) and a route for the host 10.10.0.112 only. The client can of course override the configuration sent by the server and add some of its own, e.g.:
It's unlikely the network would be the bottleneck here, but the HDD might be.
A typical 7200 RPM HDD will deliver a read/write speed of 80-160MB/s.
On the other hand, a typical SSD will deliver read/write speed of
between 200 MB/s to 550 MB/s. (TekHattan)
Windows Explorer could be a culprit, too, but it usually slows file transfers down when copying ...
When you say your broadcast is 192.168.255.255 do you mean your subnet?
if your subnets are not configured correctly they can cause connections issues also if your devices are having an issue by be leased the same IP can cause this conflict.
I am not the wiz or master of network configuration but I just spent the past 4 months dealing with situations like ...