Hi, Sam! If you are planning to fly x-country, a half mil works just fine.
The more detailed map doesn't have airways adequately displayed, as you will most certainly be working a height band between 2,500 to 6,000 or maybe even better with a bit of wave action.
GPS is lovely but you need to carry the half mil map. Ask an experienced x-country pilot to show you how to fold it. So you don't have to wrestle with it in the cockpit. I always cut off the parts I am very unlikely to use with my glider, such as the Irish Sea, the English Channel, etc. And save separately within reach the list of aerodromes and their frequencies, in case you need to radio for permission to cross airspace, or to land.
Mark with a chinagraph pen your proposed route, and on the final glide, the heights you need to make it home after that last climb, in case you need to top up.
All the fancy flight directors still wont help you follow the energy if you don't study the sky.
Have fun!