1... IBIS isn't a big factor is size. dSLRs with IBIS don't weigh any more than dSLRs without IBIS. Yes, it has caused the A7rii to be a bit bigger than the A7r.. but the complaint isn't those 100 grams. It's in looking at an entire camera bag, there isn't much difference... whether 5000 grams, 5200 grams, or 5300 grams.
I've shot plenty of cameras with and without IBIS. It's far less of a factor than it was years ago, as more and more lenses are stabilized. (and a stabilized lens can actually be far better than IBIS). I recently replaced my unstabilized Nikon 50mm and 85mm with stabilized Tamron 50mm and 85mm lenses.
My only unstabilized lenses that I use, for Sony and Nikon, are:
A -- Rokinon 14mm/2.8 -- manual focus as well. But as such a wide focal length, it's rare that stabilization would make much of a difference in getting the shot. If it's truly dark, I need a tripod either way. And if there is adequate light, I can already use a pretty close shutter speed -- 1/30 handheld without any trouble.
B-- Nikon 18-35. Same as above.. wide enough, that I don't really miss stabilization.
C-- Sony Zeiss 24/1.8 -- With an effective focal length of 36mm, this is the longest unstabilized lens I use. I actually do feel it would benefit from stabilization sometimes. But I don't think I'm missing many shots.
That's it -- All my other lenses are stabilized. For Sony, 10-18, 50/1.8, 70-200/4 -- all stabilized. For Nikon -- 24-70, 70-200, 45/1.8, 85/1.8, 105/2.8, 300/4 -- All stabilized.
2 -- Yes --- Maybe the more expensive Sony lenses are "better" in some cases. That said, sometimes it is nice to have options so you can balance price and quality. I'll use ultrawide as an example -- Nikon has 3 ultrawide zooms, as well as options from Tamron, Tokina, etc. The Tamron 15-30/2.8 is $1200. (it's 2.8 and it is stabilized). The Nikon 18-35, which has very good IQ, is only $750 -- is you don't need super super super wide, or stabilized or 2.8. Point is, you have options, at different price points. The Sony 16-35/4 is $1350 -- So if you are shooting Nikon, for $150 less, you can get a lens that is slightly wider and 1 whole stop faster. Or, you can get a good light lens that is $600 less, if you are willing to go unstabilized and not quite as wide. All 3 lenses have exceptional IQ. So even if the Sony 16-35 is a tad "better," a rational shooter might still prefer to save money with the other lenses. A Nikon or Canon shooter has lots of 85mm options for under $1,000 -- The only existing native options for Sony are both over $1000. Is the Batis 85/1.8 better than the Nikon 85/1.8g? It might be a little bit better, but the Nikon 85g is rather exceptional itself, and $700 cheaper than the Batis.
3-- The "F" menu and customization makes it pretty easy to get to most features. But when you need to change a less common setting, it can be a pain in the butt. I was doing long exposures at Universal... realized I was getting motion blur despite being on a tripod -- DUH, I need to turn off steadyshot. Took me quite a while to figure out where Steadyshot was hidden within the menus. Nikon's menu system is a whole lot more logical.
Hogwarts Castle
Universal's London at Night
I'll post a photo once I get it.
Hogsmeade
