I put every ounce of cash I have available into the brokerage account, because I have a risk allocation that is relatively risk free, and generates close to 10% in interest per year.I want to invest in a rental home.

The general partnership structure may vary from one deal to another but what we regularly see is 30-35% of the GP allocated towards the capital raise (which is what you'd be doing).

Is it permissible to use the allocation of building to land from the county property tax assessment instead of an appraisal? 

Example: Directly related- Replaced carpet in 1 of the rented rooms : $500 Indirectly/whole house- RE Taxes $6,000 but only $3,500 is business related based on the allocation. 

Until you allocate your expenses to each apartment, nobody can tell what your ROI is other than in gross, which means you cannot improve on your performance and estimating.

Most people assume this cost will be covered in their 5% CapEx allocation but it isn't.

If they are simply a contractor and no partnership is in place - you would just pay them more in cash and report the amount on 1099-MISC.If they are a partner in a partnership - it gets a little bit tricky as normally allocation of income/expenses are dictated by the partnership agreement.

[MP] Taxes you deduct when the bill was paid, and you will subtract the credit for taxes allocated to the seller. 

I guess it is a number thing, which leads me to one last question (I promise not to bug you too much):  How do you allocate your time efficiently; is it heavily invested in crunching numbers and finding the right piece of property to invest in, or do you spend more time on the rehab component of the project itself?  

There are many ways that the IRS has deemed appropriate to allocate tax basis between building(depreciable) and land(non-depreciable).One method is that you may want to see the ratio of land/building allocations of recent homes sold in your area.