Newbie query re OS use

I do a quite a lot of rambling using books, compass and OS 1:25000 paper maps, plus a lot of intuition in places . I am beginning to think that GPS/WAAS could usefully replace the intuition bit. After some lurking, I am getting the idea, but have two queries:

1. am I right in thinking that
a) I can use PC software to correlate OS 1:50000 on screen with the 1:25000 on paper and download waypoints to a weatherproof GPS device, and
b) set up the handheld so that it will show where I am using OS coordinates and a bit of the 1:50000 map?

2. What is the minimum setup that I would need to do this?

Thanks in advance.