Hah, literally the longest active thread on the forum is about multiple iron farms on Bedrock. It's a good read.
The short version: stacking villages on top of each other does not work cleanly in Bedrock. FlnDutch and others are making good progress figuring out a possible way around that (see that long thread), but no full solution has been found yet.
At the moment, if you don't want to build a chained village farm like Gruva Guy's, your best bet is to go for horizontally-spaced farms. In that case, if you build carefully you ought to be able to have the village centers 65 blocks from each other without trouble. There is some weirdness about how Bedrock adds doors to villages, though, and if it were me I would make it 65 blocks from the nearest door of Village A to the center of Village B. This makes sure that a newly-noticed door in Village A (when a villager sees it) will not be added to Village B instead.
If you want to be absolutely certain (and easier to measure perhaps), make it 65 blocks between the nearest doors of both villages. Should give you plenty of room and even with the minimum simulation distance of 4 chunks you ought to be able to AFK between them and they'll both continue to produce.
Keep an eye on that long thread, though. Some dedicated testers are approaching a stackable farm solution.
My question is whether or not when an entity (such as an item) travels to another dimension (such as the nether) and if the player is not present in or near the chunk(s) were the items originated from, whether it keeps those chunks loaded due to entities coming through the nether portal as it does on java edition? This would be very helpful as the system that TangoTek is using to keep his iron farm loaded (snow golem throwing snowballs through the portal; aimed at a endermite) could work if this property even exists without using cheats? Thanks!
My understanding is that that technique does not work on Bedrock. Outside of your simulation distance (and without enabling cheats and setting up a Ticking Area), the game simply stops processing anything. The snow golem, for example, would stop throwing snowballs once you were out of range, and start throwing them again when you got within the simulation distance.
Other chunk-loaders, like minecarts or hoppers, don't work either, as I understand it. They just stop working once they're outside of the sim distance.
The only solution I've seen (and I have not thoroughly researched this) is to log into your world on a different device - a phone perhaps - and leave that Steve in the area you want to keep loaded, while Real Steve goes out exploring.