I've run a couple hydro setups on two vehicles, one being my 4runner with LT and one being my 4500 solid axle Land Cruiser. Couple of points before I get into specifics and for people who are tl;dr: I HIGHLY suggest hydros, I have yet to see a situation besides packaging where they are not vastly superior to a normal bump. You can change the length, change the compression easily and on the fly, take it apart to heavily change the internal valving, rebuild them, etc. The mere ease of tuning them which anyone with a compressor or nitrogen can do alone makes them a worthwhile investment for someone who doesn't want to tear their shocks apart and valve their suspension. Everyone bottoms out at some point, hydros give you lots of control and arguably the best way to slow the suspension down before hurting yourself or your truck.
On the 4runner I ran 2" 2.0 FOAs up front off the lower arm. I ran them around 300psi which worked great, I honestly can never say I heard or felt them engage--the transition was very seamless (though I had lots of other shit making noises). I also got a set of 4" 2.5 FOAs for the rear which I then shortened to 1.5", this was a huge band aid because I thought bumps would help with shitty shocks when I should of gotten good shocks and left the stock bumps. I shortened them with a PVC spacer, which worked fine and fit really well (I wouldn't do that again, but if you don't have access to machinery it worked fine). I ran from 150psi which was very clanky as some people mentioned, down to 60psi which I couldn't hear engage and still served itself well. I tried bumping them to 150psi with a CO2 setup a few times but that didn't seem to do much if anything, though that might of been user error or a phase transformation of the CO2 under the high pressures of the bump (?).
On 4508 I applied what I learned from my 4runner and went with 2" 2.0s. Anything more than 2" for low travel numbers (ie sub 16" probably at the tire) starts to have too much effect with the suspension when you don't want it too. Figure a 4" bump with 16" of travel is a quarter (25%) of your entire travel range is just bump travel, which means your suspension is now heavily pushing back the tires and trying to keep you from slamming down so if you had only another inch or two of that whoop left, well now your compression stroke is slowing down and the whole chassis is getting pushed upwards a lot more than if the shocks alone were allowed to do their thing. Likewise, a 2.5 is an absolute monster of a bumpstop and not worth the weight and size on anything except maybe TTs and Rock Bouncers and Monster Trucks.
On 4508 I ran the hydros straight to the axle. The whole time I ran 100-150psi iirc, I think I started at 125psi and bumped up to 150psi while tuning at KOH since the suspension was feeling really dialed but I was bottoming the hydros out a hair more than I wanted. My current opinion is the "ideal setup" is where the hydro CAN get used for normal stuff, but not fully used ever. That allows that last inch or so of bump travel to only come into play when you are really pushing the truck more than usual or hit something unexpected. I used to be of the opinion you should never use any of the bump unless you hit something gnarly, but after a bunch of tuning it felt good to me when about half the bump was frequently used. This was for larger whoops, and barely kissed if used at all for normal whoops, and then like I said a bit left in reserve for unexpected stuff.
My new 4800 buggy build will run the same 2.0 2" hydros from 4508, and will obviously be a solid axle car. I may increase the rear to a 4" bump since the rear will ideally be pulling 20" or more of wheel travel but we'll see.
My buddy Cartzo has some hydros on his front LT setup on his 1st gen 4runner and they bump off the upper arm uniball cup (it runs a horizontal upper uniball) which I think is one of, if not the best way, to bump off a IFS setup since you can tune it a lot better since there isn't a huge lever arm acting against the bump plus the bump loads are transmitted straight through the spindle instead of applying a bending moment like if you bump off the arm. And since there's no lever arm, it's not like you're running a tiny stroke bump to get the bump travel at the tire you want.