I'm going part-time. From my full-time schedule to 24hours/week.

I haven't negotiated everything yet with my employer, I've made propositions about many things. But I see nothing in the employee manuals about Part-Time employees earning any Vacation time, nor getting any pay for holidays even if normally working on that day, and the doors are closed. When I say Holiday pay, I mean getting paid for the hours you would normally work on that day or maybe 4 hours or something.

Are there any laws in Michigan/Federal that govern Part-Time employees on whether they get any rights to Vacation time, or Holiday Pay?

Sidenote:
When I worked Part-Time at (grocery store), or when my wife worked part-time at (deleted)years ago, we would both get as a part-time employee 4 hours pay automatically even if not scheduled to work that day. Also I earned more vacation time as a PT employee at (grocery store) than I did as a FT employee at my current company. But I'm guessing none of that stuff is required, just maybe because of the Union at (grocery store) and just because they feel like it at (deleted)?

Short answer, no there is not.

Considering that federal and state laws don't require vacation pay or holidays for full-time employees, you won't find any laws protecting those kinds of pay for anyone working less than full-time.

This will be strictly between the employer and employee, unless there is a collective bargaining agreement in effect.

No state requires that any employee, full or part time, receive vacation pay. There are three states, none of them Michigan, that have limited holiday pay rules but only regarding employees who work on the holiday - no state has a requirement that any non-exempt employee, full or part time, receive paid holidays off.