Wheel and backspacing questions

I know I'm asking about a pre Tacoma Toyota, but I'm looking for wheels from this era so figured y'all might be the people to ask. Ive looked around and haven't been able to confirm what I believe about these, so please correct what is incorrect written below. And please read the last question, what's the difference between the 16 and 18 hole versions???

I understand backspacing and offset and the difference between them. I will reference backspacing here because those are the numbers I'm going off of, but if somebody here has info for me and it is in terms of offset, that'd be great, I can do the calculations to convert it to backspacing.

Please correct me on any of this:
I am getting 16" wheels for my 88' pickup, and will transfer them later to my 92' pickup (both 4wd). These both have the same stock backspacing of 4.5"... correct?
I believe I would want the same backspacing as stock, I don't want them to stick out any wider than stock, and am not worried about rubbing, as I've skinnied up from the 235/85r16 I used to run to the narrower 215/85r16 pizza cutters that will be on these rims.

It is my understanding that the 96' to 02' factory steelies (from Tacoma's, 4Runners, etc.) have that same backspacing of 4.5". but then after that, they started making them with the oval hole around the valve stem, which signifies later models and they have a larger backspacing of 5.25" moving them slightly more inward.

Questions: Is all this above correct so far? If so...
Am I correct to assume I'd want the same backspacing? (even using the none abtrusive tires I mentioned) and if so...
Am I safe getting any that do not have the oval valve stem hole? (I know how to read the serial number on the rim with the mfg date, but people rarely have photos of the serial number and never seem to want to send a photo of it).
And for the biggest question of all, is there any difference between the 16 hole and the 18 hole versions!!!??? I haven't even been able to find if they were from different years, or for different vehicles or different markets, etc. Is there any difference other than cosmetics? Can you run a mix of the two at the same time?

Thanks a bunch! I look forward to hearing from all the backspacing/offset experts