In reply to RG:
If you want to be remote (in UK terms) I'd recommend Knoydart. Check with the Knoydart Estate first to ensure that there is no stalking - I don't think there is in April, but you should notify them out of courtesy. Get a fishing boat (ferry) from Malaig (Railhead from Fort William) to Inverei.
It's very mountainous. From there you can work out a number of routes to suit your ability, fitness and time table including walking out to the railway line and station at Glenfinnan.
You have the options of camping or using bothies. It is a magical and truly remote wilderness. NB There is no continuous "trail" per se, although in places you can follow sections of land rover tracks. Elsewhere there are few defined tracks on the ground and you need to be good at map reading and navigation. In places you will have to wade to cross rivers. Even in late April there is the possibility of snow, so be prepared to have to alter your plans if you have no experience of mountains in winter conditions.
On a completely different suggestion the southern section of Offa's Dyke is both challenging and in places surprisingly remote, particularly over the Black Mountains. There are a few roads and towns/villages, but the former are mostly quiet and the latter few and far between and very picturesque. You can B&B or camp with discretion.