Rans6,
Since installing SkyDemon on an Android tablet I have never looked back as far as navigation for both VFR and IFR flying goes. I still carry paper maps and plates in a bag behind the seat of my Archer but for all intents and purposes I run a paperless cockpit apart from the SD printed pilot log that I produce pre-flight. Initial subscription sees you right for a years updates and you can add Pooley's and AFE's guides to be included. Total is still less that £200 which is really only an hours flying to many. Like you I have a Garmin to feed but I tend to update that twice a year unless I'm planning any IFR work.
As far as which tablet I think most people will lean towards Samsung products, but I do tend to feel that the latest ones are a little flimsy for constant use. Believe it or not I use a 'Tesco Hudl II' still available for less than £100 on ebay and use a 2.4amp charger to keep it topped up in flight. It has yet to let me down in any way and is still one of the highest performing Android tablets available. It's built like a brick and has yet to suffer a scratch despite knocks and drops. That said, I back it up with an older Sony Xperia 10" which I find a little too large for anything other than putting on a lap board. The shiny face is also a disadvantage in sunlight, but at least it's a back up.
As for mounts I have the 8" Hudl on a RAM mount on the column and it sits nicely between the yokes.
Until they standardise on what protocol to use for proximity awareness I am sticking to radar or eyeballs for separation but I'm sure you will get replies from the geeks who are already ahead of me on that.