You should look at your whole financial picture, create an asset allocation strategy/plan, and then determine if you should invest the whole 300k in real estate.

little do they realize how much it can cost.Anyways i am starting to look into smart water metering so i can divide the quarterly bill and allocate it towards their water usage. 

To allocate income/expense to each property on Sch E (as I have done so far) or2.

As a private investor all my money is allocated.  

You will allocate the sales price between the building and land.

This is our first BRRRR so we are still working out the numbers and how much to allocate for each of the main expenses like Vacancy, Maintenance, & CapEx. 

It is my view that the duplex when properly allocating for maintenance/cap ex is not going to have any income this year. 

In my experience, the 50% rule would include vacancy, management fees, capital allocation, etc.

I calculate that with $250 per month allocated towards repairs and CapEx, $100 per month for vacancy, the $590 per month in utilities insurance and taxes, and about $160 for a mortgage payment ($25,600 at 6%), I would still cash flow almost $300 per month.

Generally you would do an allocation of your purchase price to the land and building portion based on the allocation done by the county property appraiser.As to your question about hiring a CPA, I am probably biased as I am a CPA, but I think ultimately you need to do what's best for you.