I own investment properties in Ohio. Each property is under its own LLC and bank account.

My question is, does it make sense to setup another LLC as a holdings company (parent company) which will then own the other LLCs (subsidiaries)?

If so, what are some of the tax benefits that may come into play with this strategy? Should I use the holdings company as a ‘management company' (managed by me) and have each property's LLC pay the holdings company a management fee? Maybe should I own them with a trust instead?

Some of my properties are rentals and some are flips. Any insights on how to best take advantage of tax laws is appreciated.

Unless you elect to treat the LLCs as corporations for tax purposes (C or S) they are treated as disregarded entities for tax purposes (which means the management relationship would also be disregarded for tax purposes) so in effect the tax consequences would be no different than holding the properties directly in your own name. 

@Alex Bernot

Your questions cannot be responsibly answered without an extensive discussion of your real estate business and your overall financial situation. It is case by case, and what works well for one investor may not work at all for another. If you want real help, you'd be well served by finding your own accountant to guide you with tax planning.

That said, some general pointers that also may or may not be applicable to you:

• You usually want to separate rentals from flips, both for tax reasons and legal liability reasons
• Keeping each rental property in a separate LLC is debatable; it does not usually change your taxes and is intended for legal protection which is for attorneys, and I'm not one of them
• Ditto for trusts
• Keeping each flip in a separate LLC is usually counter-productive but is also case-by-case
• Creating a holding company to own other LLCs may be a bad idea from legal protection angle, but it is also for attorneys and not for me
• Creating a management company can unify and simplify your operational procedures, depending on how you run your business
• A management company can also bring certain tax benefits such as generating active income and room for retirement plans and other benefits, however you may already have this option via your existing LLC(s) involved in flipping

As you can see, there's no quick microwave recipe here. 

As already mentioned before, you would probably want to have different tax status for your buy and hold vs your flips.

For asset protection purpose, you have two main threats: inside liability and outside liability.

The inside liability protection is equivalent in every state, however the outside liability protection varies greatly by state.

That is where using a holding LLC in state where a charging order is a sole remedy can help as any outside liability claim would need first to go through the holding to reach the sub LLC. I believe Ohio has good charging order protection already, so it may not be needed in your case on that point.

Also, if you want to have a partnership for estate planning purpose, it make sense to have all disregarded LLC owned by one holding to only have one tax reporting for the whole structure instead for each sub LLC.

Usually, a management entity is an active business and would better be taxed as a corporation to get all its fringe benefits. It is often recommended to keep the active business completely separated from the ownership entities to add another layer of asset protection. So in my view the holding should not be the management entity.

Again you would greatly benefit to have a strategy session with a real estate, asset protection and tax attorney to discuss your specifics. Most of the major firms that are often mentioned in this forum offer a free initial consultation. 

It really depends on what you are using them for and what your goals are.

Such solid advice from @Michael Plaks . That is a must read post for so many investors.

This could make sense. You could possibly put them all under the one LLC and claim them as business expenses to the main company. @Alex Bernot

@Alex Bernot find a niche service provider that integrate their tax and asset protection. The big firms likely will push you into their structures. Your structure and plan should be highly customized, individualized and make financial sense for you

@Alex Bernot

If you create a holding company - What added benefit(tax/legal) are you getting?
Would having an extra holding LLC give you added tax deductions / legal protection that you are not getting already?

Regarding having a management fee structure set up - you should have a strategy for doing so. 
The con with this strategy is that you are converting income that is rental in nature to ordinary income(may be subject to SE taxes).
The pro with this strategy is that it potentially opens you up to health insurance / retirement account deductions.