I recommend IPCop over Smoothwall. This old SecurityFocus article
gives a good introduction:
IPCop is derived from the SmoothWall project but was forked as a separate project for a two main reasons:
* To provide better, and more friendly support. Because the SmoothWall authors have both a GPL and a commercial product, it is obviously in their interests to support the commercial version more than the GPL version. The IPCop authors are providing support for a GPL product.
* To provide some additional features. There are some additional features planned for the commercial version of SmoothWall, which the IPCop authors have plans to implement in their GPL-ed product.
As you said, it's also easier to install addons for it (IME, anyway).
If you set up a VPN, you would be able to access your network shares from a remote location if you connect to the VPN. The VPN effectively allows you to connect to your home network even though you're not there, so you'll be able to access them just as easily (or otherwise!) as ever.
It is quite easy to configure them on IPCop. Take a look at this tutorial: http://www.taupehat.com/vpn/