Windows 7 File Sharing Workgroup Locally & via VPN

windows 7 with powerful machine i7, 8-core, 16-gb mem, ssd
apps: intuit tax pro series 2012 down to 2010
one local client connection
two remote client connections via vpn
vpn router: asus rt-n16 wireless router 300
experience index with vpn router:  very fast
vpn client connection done in couple of seconds
application run via vpn takes 4 minutes at most to load data share
when data is loaded on tax proseries it's normal operation
secured authentication 128-bit, chap2 only

problem
although this is not an ideal or even advisable vpn environment but it works.(windows server 2012 with essentials is still in the making on a trial basis but is soon to come as owner approves budget, if ever he would because of expensive cost. however tax season is just about a week to go, owner wants this launched.)
proseries approved configuration: LAN. this is a lan albeit added vpn clients. all the same they operate within the shared folders. my problem is the security risks. how could i minimize the risks of data corruption? please tell me the most effective way to monitor the endpoints. any better than spiceworks. use this system but do not know how to effectively set the monitors and logs and triggers to alert on vpn intrusion or abnormality.