Most of the clients I've worked with as a Realtor are investors and I've already spoken to them about partnering up and helping out with the financial aspect (Hard money loans), I can handle finding the deals and working with the GC's.I am really excited to get started on my real estate investment project, but I am struggling with calculating the costs associated with holding the property.

You need to make Estimated Payments to IRS if your W2 withholding is not enough to cover the amount discussed below. 

It formalizes the repair requests so a tenant can't withhold rent or sue with a claim I didn't fix something they never told me about or they claim there was some problem that never existed.

There are also co-op sponsor units which can be sold with holder of unsold share rights which allows the purchaser to rent out the unit indefinitely as long as they don't occupy the unit.

I typically withhold 10% for maintenance, 10% for vacancy, and 10% for property management. 

To get a W-2, you would need to form a C-corporation, make yourself an employee, and have the corporation pay you while also withholding income taxes, FICA, SUTA, etc.This leads me to a more simple plan: if you insist on an LLC, you'll have to report the income on your personal return, so a bank will see the income anyway.

They would likely be subject to FIRPTA withholding issues that can complicate the timing issues involved in a 1031 Exchange, but you can file for an exemption with the IRS and get the withholding requirement waived if doing a 100% tax-deferred exchange into other U.S. property. 

So don't withhold rent, or you could be filed on for eviction action, and or charged late fees.