Havn't read all this thread and don't know where you are or if South Wales caves are close. But I pick up you have done climbing/absailing. To do 'interesting' caves you want to know SRT which is probably slightly different to what you already know. At risk of getting flamed my warning is a figure 8 is not an absail device - it is a suicide device - when I see one I start shaking with fear! They are not hands free and should be avoided. A rack, whilst not exactly hands free is easy to use - best for long pitches and easy to do smooth descents. A stop descender is hands free (ie. take your hands away you go nowhere), harder to do smooth descents and if you suddenly become scared you might squeeze the handle rather than let go of it - so you will get more scared until you remember to let go. Make sure you can change from descending to ascending confidently and easily before you forget to tie a knot in the end of a 20m rope you throw down a 60m pot!!! it has been done with bad results
The 'big' beginners cave by here is Eglys Faen - big (long) easy cave. A cave that is really nice and not too hard is Ogof Nant Rhin (excusse bad spelling)
Once you happy with srt Nant Rhin has a scond entrence - Pont Gam - tight, grabby, sharp, muddy but very satisfying.
You want big caves we got em in the Clydach Gorge and surrounding area! but they are not really first time caves. Wherever you go especially if you go solo, try to find a survey and description of the cave so you know what to expect. Most of my caving has been done solo - starting with 'easy' caves I've worked up to challenging caves by using descriptions to get to 'next step'.