Those are certainly realistic and not unreasonable hurdles, and I don't disagree with you at all.
I think if the mall and adjacent businesses were to provide some corporate sponsorship and partnership then this would have the ability to clear some of the hurdles with dollar signs (insurance, infrastructure, etc.)
I'm sure just running the Budd car in the start would be fine, at least to see if the service would be feasible and to give the public a taste of what was being offered. Start off by offering an hourly, maybe ninety-minute shuttle between downtown and the crossing adjacent to Chuck's with a shuttle to the mall. If it becomes popular, explore restoring the track immediately behind the mall for a closer walk across the parking lot, and if that becomes a reality then I think an extension to the park and ride off of 202 wouldn't be a complete foamer's dream.
The college is across the swamp from the mall too, so I wouldn't see the harm in approaching them to explore providing rail access to downtown for their students.
I think if the HRRC hurdle could be cleared, then Metro-North and P&W might be willing to let this be a thing. The crew experience can be gained, and equipment could be repaired.
This is a total foamer dream, but again, I don't think it's completely unreasonable.
"That sapling that once grew just south of Wassaic may be long gone, and the Harlem Line’s appearance may have changed over the years, but for decades to come, I can count on it continuing to provide me with funny recollections"