Keep it all on the server and RDP for access, 400 meg is a fairly large file for QB, you do not need a file that size crossing the network to open....
I have QB on a few terminal servers, RDP is plenty fast ( that is for QuickBooks) with a decent server.
The issues with TS are you need a good bit of ram (8-12 gig min (opinion), a fast CPU, besides a reasonably fast disk subsystem. Raid 1 for safety, raid 10 for extra speed. You can't skimp on the CPU speed or the amount of ram. The disk subsystem affects the initial loading primarily in TS, with sufficient ram it basically runs in ram after that.
On the other side of the coin, I have a client with a T110, over a year old, a bare bones very basic server, 8 Gig ram, 500 Gig SATA drives in raid1 (approx. $ 1300.), running Win2008 R2, Terminal Server Gateway and Terminal server with a small QB file for a couple users. Fast enough for them but could be better. This was purchased with everyone knowing it would not be super fast, though it runs QB faster then any wks at the client's office.
If you consider RDP, remember to figure in licensing costs
Security....
If it is just for internal use, terminal server is fine. If users will access QB / other programs from outside the network I highly advise setting up TSG for SSL security. TSG and TS can be on the same server in a workgroup setup.