Mining out a new map entrance/exit for travellers

[Willheart]

I found a few threads on the topic but I'm still not 100% sure on the rules surrounding it. So my map has 3 exposed sides where travellers/raids can come from and a blocked north mountain where my base is.

1. If I mine through completely and make a tunnel to the north edge of the map, will travellers start spawning at that northern entrance, and/or try pathing through my base to reach it as an exit?
2. I know travellers can use my doors, but on a different playthrough they seemed to prefer exits without doors obstructing (I blocked off an insect cave with doors), if I want them pathing through my base should I keep an exposed corridor? Will 'forced open' doors count?
3. Are there any requirements how many exposed tiles need to be connected to the 'abyss' edge of map for it to be considered a map entrance/exit? Does it matter if it's in the middle or skewed off to the corner? Somebody said raids can't spawn underneath mountain roofs, so would only travellers spawn there?
4. Also, since it's so close to my base, will raiders (and travellers I guess) prefer to spawn at the entrances farther from my base, or is it equal chance? If mountain roofs do prevent raids spawning, will using devmode to remove it allow raids from there?

My intention is to have like a rest stop trade outpost through the mountain where most of the traffic funnels through my base, with hospitality, traders and travellers I expect it to be pretty lively and maybe a little hectic if I have hostile factions all trying to share the same road, but it gives me an excuse to convert some ideoligions, maybe harvest some non-essential parts, make some brainscans, etc, before releasing them in good health for a relation bonus.

Bonus questions 5. Are faction ideologies permanent? If I convert many people of a faction to my ideologion, can this cause the faction to change it's ideologion to mine? Alternately if the faction leader dies (or I happen to convert him) does this have any changes to faction ideologion?
6. Is faction leader replacement just a randomly generated pawn or can it be chosen from pre-existing faction members?
7. Any way to choose/pressure where traders decide to hang around? Is there a favourite mod for this? Seems like it's usually just any random spots outside home area, but that inconsistency isn't always be convenient especially when there's a big river outside.

Obviously I'm using a fair few mods, but nothing to my knowledge that specifically changes how raids/travellers spawn in though, so I'm assuming it's vanilla behaviour (or rather let's assume we're running vanilla).

I would appreciate some clarity, even if it's just anecdotal experience, since a lot of the threads I've read up on are many years old, and If I want to design my base properly these answers will seriously change its layout...