Fermi
Have a look at this online map to show you the footpaths etc - just type the nearest village name into the search box on top left.
There are several different map views but I tend to use the split screen (OS & Satellite). As you follow the footpaths with your mouse on the left hand map you can follow it on the satellite view (which will give you an idea where the caches are when comparing it to the geocaching google map.
Letterbox Hybrids - as far as I am aware (I have only found one - for a challenge cache), the only difference is that they contain a stamp (and possibly an ink pad). You can use this to stamp your own book (if you wanted to collect the stamps) and stamp the logbook with your own stamp (if you have one). Otherwise, I think they are pretty much the same as a traditional cache ... but I'm not sure if they contain swaps or not. And yes, no reason why you can't do them one or a few of them... without doing the whole series.
Letterbox (popular on Dartmoor) - I think these use clues/map references/church spires etc rather than GPS coordinates. (but never looked for one so not 100% sure).
Have fun.
GAGB member since 2005
GAGB Committee member 2010 to 2016 (Chair 2012 to 2015)
UK Mega Event Chairman 2009 (Weston-super-Mare)