Remember, I would normally never need any more VPN connections than three. (usually only one, possibly two)

Bear in mind that these are *simultaneous* connection licences, you can have as many client PC's configured ready for VPN as you like.

I see the 150 only supports site-to-site VPN tunnels (which is what I need I think), and optionally also Global VPN account licences (what is this?).

Site-to-site VPN is for a semi-permanent "nailed-up" VPN connection between 2 remote sites - you don't want that. Group VPN is what you will be using from your remote PC.

If you're contemplating buying new then give www.tekdata.co.uk a call - their support people are very clued up on Sonicwall products and they may even save you buying more than you need.