If it's not for you, then don't make changes to suit your OCD. As to30" cabinets, whether to change those out depends on your local market and the expectations of your target audience. You need to know that going in.

I would do 36" cabinets + 6" of crown to take them to the ceiling.

IMO take them close to the ceiling and minimal trim I often adjust the space from counter to bottom of uppers to make that space at the ceiling only needing minimal trim. If this is a flip you have to know the market to decide if a sink centered is a must. I actually often do kitchens where the sink is not under the window since we rarely spend our days at the sink anymore. If you do not have crown in the rest of the house IMO it looks silly in only the kitchen

What's in your budget? How much will be your return on investment? The bottom line should be your focus.

You get 39" cabinets and add crown.

It's a flip. If existing leave as is. If new cabinets and redesigned kitchen, reverse engineer it. Will the additonial cost of the cabinets and labor get you a better ROI? Will it help sell the house quicker? What is the area in the way COL and other houses (high end, middle class, working class, etc.)? Context is key.

" and my OCD is kicking in "

OCD really has zero place in a flip, except to cost you dollars and less profit.

I would do 36" cabinets + 6" of crown to take them to the ceiling.

I'll second this idea. It won't cost all that much more than 30" + open space, but it'll look SO MUCH BETTER.

Agree that OCD has no place in a flip -- never lose sight of the fact you're working on this house for profit, not your own preferences.