I entered Nuka World last night. The Nuka-World Transit Center is way to the west edge of the map.
I fast traveled to the Lonely Chapel to its northeast, and just walked right up to it. There's a highway that leads into the main entrance.
I didn't want to enter the main entrance, since there were enemies there and I was using a stealth character, but I found a gap in the fence to the north of the main entrance.
Here's a video on YouTube of someone approaching the transit center from the Sunshine Tidings Co-Op. The transit center comes into view around 4:40.
No it is not. This is one reason why some people disliked this DLC (A lot of people complained on the Steam reviews about having to to make the choice of being "Completely Evil" by siding with the Raiders or "Finish the DLC very fast" through the Open Season quest).
From the Fallout Wiki for Home Sweet Home:
Preston Garvey will instantly hate the player after establishing the first raider outpost, even if his affinity has already been maxed and the United We Stand perk unlocked. This is understandable given that the goals of the Nuka-World gangs are directly opposed to the Minutemen's settlement-related activities. Even if Garvey is not the active companion at the time, he will find out about it and become hostile the next time he sees you. He can still be ordered to move to other Minutemen-allied settlements from the workshop menu.
As you can read, the Wiki states that for establishing the first Raider Outpost, Preston will immediately hate you. I think the reason why Preston will get angry is because he can also assign the Open Season quest in addition to Mackenzie. This thus makes him aware of the Raider presence at Nuka-World.
I'm sure you have looked up the perks you receive from doing Home Sweet Home, but to reiterate:
The Wasteland Warlord Perk which has 3 stages that are unlocked as you build more Raider camps. These are:
1 Raider camp gets you new structures and building items and Raider outposts.
3 Raider camps gets you new structures and building items and Raider outposts as well as Raider-themed stores.
8 Raider camps gets you an achievement and unlocks the Tribute Chest that you can build (not really a perk, but its the reward you receive).
For completing Power Play, you receive 2 perks, depending on which gang didn't betray you. The gang that will betray you is whatever gang you gave the least amount of territories (including the ones in Nuka World) The perks you get are:
If the Operators betray you:
If the Pack betrays you:
If the Disciples betray you:
You also earn an achievement for completing Power Play. It should be noted that after completing Power Play, you may speak to the remaining two gang leaders for an additional weapon (the third gang at this point has been killed off should you go through with Power Play). These are:
Nisha provides a Disciple cutlass with the Instigating legendary effect, which deals double damage to enemies with full health (I personally love this weapon).
Mags provides an Operators sniper rifle with the Relentless legendary effect, which refills Action Points on a critical hit.
Mason provides a puncturing rocket bat with the Furious legendary effect, which deals increasing damage for each consecutive hit on the same target
If you decide not to go through with helping the Raiders, and begin the Open Season quest, you can still restore power to Nuka-World. Once you finish Open Season, the doors to the Nuka-World power plant will open, allowing you to restore power (according to the Wiki).
Best Answer
I can confirm (through testing) that you will only turn nearby Raiders hostile towards you. If you kill, say, two of them that are close by and return to the city/park, they will not be hostile towards you. An interesting little tidbit is that killing a raider of one faction will not necessarily cause a nearby raider of a separate faction hostile