Hello there!
I am Belgian, 35 years, more than 20 years experience with computers and more than 10 years of real professional experience, I have worked with Nestle, Ozone, LAN10 and many other small companies, for installing, configuring, maintaining and monitoring the servers. (LAMP, exchange, VPN, PBX, etc..)
Indeed it is important to properly configure the iptables rule (but it's really easy, it's just 1 rule.. )
I would also take care of letting the squid server only listen on the local vpn interface, for obvious security reasons, the main challenge is actually to make good, secure rules on your squid server.
I would set up everything keeping a runbook with all the actions and modifications, then test everything with you, if we both agree that everything is running as it should, I would then write a procedure for you or anybody else to be able to reinstall and reconfigure it properly quickly and easily.
I am usually available between 8 and 18h GMT every day, if you have any question even outside those hours, do not hesitate to send me a message here on freelancer or on skype: protojob
Thank you for your attention, I am looking forward to work with you!