I didn't have a choice of memory--got 8 gigs, take it or leave it. But your reasoning seems sound. The two types of memory aren't equal--card memory is slower. But if the device works fine in its smallest memory configuration, then the operating system and programs are getting the fast memory they need, and you don't need to add more. The memory cards are like floppy drives: bulk storage, relatively slow access. MP3s and videos and other big files go there. Add all you want. It's cheap.

Define "pocket". I'm guessing you must mean backpack pocket if you intend to put a 10" tablet in it. My 7" tablet won't fit a standard jeans pocket. I went out and bought a couple pairs of cargo pants (include a new wardrobe in your budget), and it fits into the big pockets with an inch to spare on either side (tablet long axis aligned with my leg). I doubt cargo pants would accommodate a 10-inch device. Maybe painter's overalls? Scotty's engineer's vest? One of those front-mounted baby rucksacks could be adapted to make a nice combo carrier and platform on which to use it while walking. What a picture that makes.

You should try out the two sizes of tablets to see how the "old eyes" like 'em. The screens on the handhelds aren't equivalent to a desktop computer display. They have a much finer pitch--pixels closer together--so your expectations for a given size of display may be off a bit. I find the fact that the display is razor sharp with no visible pixellation makes it easier to squint at a small display for long periods. It looks like a printed magazine.