Bill Mack often has events at his Minnesota studio. There were a couple in October from the online activity I could see from some associated artists. You can see future events
here.
For all I know, Balldo mentioned that he has some sort of patronage deal for Bill Mack that would get him access to the studio on a semi-regular basis. But having looked a little closer at the photos April took, I think that's Bill Mack's lambo, and I think that's at his studio. Apologies if someone's already gone over the studio shit, if they have, clock me.
This is Bill Mack's studio. Rather, this is the restaurant "Camelot" that would later become Bill Mack's studio after he acquired it in the 80's:

And the studio more recently:

They really tried to give this an old-world castle look with the different colored stone on the exterior.
Here's a promotional video for his "Weekends to Remember" event series:
Looking back at the photo April posted, I noticed a few things:
1.) The flagstone pattern behind her: Google Maps does not have photos of the driveways through the gallery, and I couldn't spot anything either on the promotional materials or socials that would match that pattern. Even a cursory glance at the entrance on Google Maps doesn't look promising:

However, it is a strikingly similar pattern to what we see on the castle walls, and looks to me like a 1960's attempt at "make it look like cobblestone". Further, if this was Bill's car, we already know that
Bill parks in a separate entrance apart from where the public enters. The flagstone would be a more impressive entrance than straight asphalt that we see on the way in on Google Maps, and more closely fits what the article describes:

Not a smoking gun, but okay.
2.) Color scheme of the Lamborghini: Bill Mack is wealthy enough to spend lots of time and money acquiring valuable Hollywood memorabilia, including things like Marilyn Monroe's lipstick, and her privacy gate (see article). Affording a luxury sports car (i.e. not a rustang) is not a big deal. If you watch the promo video, you see the black and red color scheme everywhere in the gallery, but it's probably best exemplified by just looking at the guy:

Again, it's not a smoking gun, but I'm willing to bet the black lambo with the black (or blue) and red stripe is his. That's also probably the reason Balldo is coy about who the car belongs to. He and April get to giggle to themselves that they know THE Bill Mack personally and he absolutely loved her!
3.) The lamps in the background: Check out those lamps and the drive they lead up to. Globe light, with two rings holding the globe in place. They're a match for lamps positioned on the front of a building from the promotional video above.
4.) The nametags: Don't know why screenshotting a video meant I ended up with Bigfoot evidence quality pngs to add here, but look at the nametags I pulled from stills on the promotional video:

They definitely appear to be gold, and the font size and type looks like it matches the one April is wearing.
Wasn't able to find much information about the Weekends to Remember, the events page on the studio site only displays future items. My guess is you can buy a package that gets you into these recurring summer events for the year, and then you have your tickets you can rotate amongst family/friends. Kayla probably was the regular attendee until Windy Wendy showed up.