The first note is, since we are relying on our initial typing, and that self-weak immunities are a non-significant bonus, Normal is a useless addition for us. The Fighting weakness is a neutral weakness that I still feel is dangerous, as many of our threats can follow up the SE Fighting move with their own SE STAB such as Tomohawk or Tornadus. This is especially considering that the majority of Ghost types that we would be hoping to switch in against with this typing can still deal with us outside choice-locked sets, such as the two Ghost/Dragons or Aegislash.
I know its a bit hypocritical to say this immediately after saying that one immunity type is useless, but I think it is a good move to submit Fairy/Poison for this concept. I'll be answering question 7 and 8 at the same time with these cases, since the interactions between the resistances and the bonuses go hand-in-hand with these cases.
a) Can this typing set up an Initial Weakness into Color Change Resist combination?
The two initial weakness to resists here are from Psychic and Steel. Looking at the list composed by Birkal at the end of Concept Assessment 2, the most relevant Pokemon here that we have this initial weakness to are Melmetal, Gyro Ball Ferrothorn, Latios, Kartana, and Tapu Lele. (Also Future Sight/Doom Desire, but that's a different beast.)
Melmetal is probably the most worrisome threat to be initially weak to, since DIB hits twice before we change colour. Unless we heavily invest in bulk, we go down immediately. However, we can effectively wall the rest following the first hit. Likewise, if Melmetal throws out any of its 3 other moves in its non-choiced set (Protect/Earthquake/Toxic) are more questionable. However, even if the Earthquake hits us SE it is significantly less scary than the Double Iron Bash and is our safest switch in. That being said... This is probably the worst matchup we are making from our good matchup list.
Kartana hurts. Kartana does lots of damage. However, Smart Strike is only a 70 BP move, and even on a choice band set, Kartana is a lot less damaging than a non-choiced Melmetal. It is worth mentioning that both of these threats are physical as well, which does put strain on the stats stage.
The other 3 are not a significant problem. Gyro Ball Ferrothorn is relying on it running a specific not-very-damaging move, which then changes us to a typing that walls it and allows us to bully it out or set up for free. Tapu Lele is similar to Kartana where it hurts like hell to get hit, but we can effectively wall afterwards, and a Psyshock likewise relies on our defense more than our special defense.
Finally, Latios brings a special interaction with this typing. Latios' set runs Draco Meteor and a non-attacking move (Trick on choice sets, Roost on Life Orb.) This means that we have a decent chance of switching in and keeping our initial typing despite that weakness to its Psychic, and then being able to reply with an SE Fairy STAB should we choose to bring one. If we don't Latios would be wasting a lot of turns trying to change our type around to hit us SE again, which gives us ample time to setup.
Overall, it can set up from its initial weakness against Kartana, Ferrothorn, and Tapu Lele, albeit with some strain on stats. It may do it against Melmetal, but that is a very scary threat that can take us out even with good bulk on a bad switch-in. It may also do it against Latios, or it may be able to just KO Latios on the spot.
To look at the list that we have our natural disadvantage against, this does not help us deal with Magearna, Glowking, Excadrill, or Aegislash. We aren't scared of Aegislash for its Steel Typing anyways, and Cawmodore we are also weak to but lets be honest, that thing is a monster when set up that would KO us with the neutral Acrobatics anyways. However this is a list of mons that we are already weak against naturally, we are not making this matchups any worse. The only disadvantage here is Melmetal's DIB.
b) Can this typing set up a Initial Neutrality into Color Change Resist combination?
The relevant initial neutralities here are Fire, Water, Electric, and Ice. Switching into Poison means it will stay neutral, because we don't change to mono-Poison. Coincidentally, the only relevant poison type is Nidoking, whose Sheer Force means they won't change our type anyways. (Also they would just use Earthquake either way.)
There are a lot here that we can deal with nicely, but I think the most important ones to mention are Dracozolt, Cyclohm, and Tapu Koko. Currently, we have good matchups against these two by switching into their electric spam. However, if instead we switch into a Dragon or Fairy move from these two, we have a new advantage from the Fairy typing. Our immunity to Dragon means that we are not scared of Dracozolt or Cyclohm in any capacity (other than Static I guess if we use contact moves), while our Fairy/Poison mix means that we can keep our Poison SE STAB should we choose to bring one to take out Tapu Koko.
c) Does this typing offer consistent switchins, that is, Initial Resistance to Color Change Resistance interactions?
Grass and Dark are the two we will always resist. The most interesting matchups to talk bout here that benefit from this dual typing are Jumbao and Hydreigon. Jumbao we would normally wall from grass spam, but if we switch in against a Fairy move we have a 4x effective SE Poison STAB. Likewise, Hydreigon is sometimes a threat and sometimes not, but the Dragon Immunity from Fairy means that we will always be able to get a free setup against Hydreigon. Or we can just nuke it with a 4x effective SE Fairy STAB. Would we bring both stabs? Probably not, so one of these is a free setup that we wall, while the other we can delete on switch in, doesn't matter which.
Something interesting is that this combo turns Fairy into a self-resistant type in effect. If we get hit by a Fairy move, we stay Fairy/Poison and stay resistant. I know its not an interaction with Color Change but rather an interaction in spite of Color Change, but these kinds of keep-the-dual-type interactions are very important to consider here, and this is a pretty fun one, adding Fairy spam to the list of things we wall unless the opponent wants to spend 3 turns shuffling our typing around, after which we will have already setup and are ready to start sweeping.
8) What further bonuses does this typing offer
In addition to the Fairy/Poison STAB interaction, or the Dragon immunity, we are neutral to SR and immune to all forms of poisoning, which helps a lot in many matchups like Amoongus or even Melmetal as mentioned above.