I need to setup 2nd site for around 15 users

Budget is limited and a ADSL connection will be used
currently the main site has 25 users

I'm think of adding a small server to host a 2nd PO and a GWIA for outgoing

Any problem with this ?

I also need users to access files from the Main site (Word, Excel etc) - is Filr a good option?

What I'm not sure about is what happens with Files which are being used by someone else ?

or should I be considering other options like Site-Site VPN ??