You can allocate a chunk of your cash one property, and then it frees up again a few months later (hopefully with a nice return included) for the next project.

Make sure you are allocating funds towards phantom expenses such as repair, capex, vacancy and property mangement fees.

This is the (rare) allocation of investors in REI. 

Start by doing an inspection of the unit, reminding people to only park in their allocated parking spots and that under the terms of their lease they are only allowed to have the people listed on the lease living in the home.

Be sure to allocate debt basis accordingly as well for all partners.

For allocating expenses, I wouldn't use a random percent, use specific sqft/percent. 

I don't have it down to an exact science by any means, but I use QuickBooks to keep track of what cash is allocated to.

As to usage, the fairest allocation method would be the number of tenants.

One option to fairly charge tenants for gas usage in this situation is to allocate a base amount to each unit to cover heating needs during the winter months.

We have paid the monthly water bill since then, but want to transition to having the tenants pay their own water usage using the RUBS/water allocations since each duplex is on a single shared water meter.