If you are connecting your network to the Internet, I would not recommend that you do all of this on the server, as you will need to connect the server to the Internet directly, and that will make it vulnerable to attack. I would highly recommend that you purchase a firewall appliance, or a router with firewall capability. This can also terminate the VPN for your remote users.
If money is really tight, then there are quite a few cheap firewalls out there. The Draytek firewalls are very cheap and I have heard good things about them (for the price). Not used them myself, but then I mostly recommend Cisco as I know it works, and know how to get it working ! The Cisco is more expensive, but in my opinion it is worth the extra for the quality of support and you can always find someone to configure it (you could even ask here for an example) or look on the Cisco website for cookbook example configs. If you are looking at the Cisco option, then the ASA5505 is the one I would recommend. It will do everything you need it to do now, and will also when you company gets a lot bigger (which it hopefully will in time).
Someone else here can advise on the server side of things, as that is not my area of expertise !
For Microsoft Office, you should look into a Microsoft value licensing agreement to save you some money. Software Assurance is expensive, but a very good idea so you can continue to upgrade to the newest versions of Office without an upgrade cost. You just need to continue to maintain your Software Assurance contract.
For a server, you should look into Microsoft Small Business Server (SBS) which incorporates email, web development, and an active directory domain. It is a very good package for small businesses that need several applications in a single bundle.
You should look into purchasing Office and the server all together to leverage the benefits of a Microsoft value licensing agreement. HP or Dell would be able to help you with both the office licenses and the server.