Governments tend to spend more on military budgets and overseas aid and less on domestic expenditures. 

If raised then you will definitely need to consider the insulation under the house as well to ensure the expenditure results in the efficiencies you are aiming for.  

What you have left needs to cover any capital expenditures or special assessments you may have over time.

Another issue that could be considered a downside is if the property is so well-suited to HI that it really can't be anything else without massive capital expenditure to convert it.

For example, it's usually safe to estimate a 5-10% vacancy rate (thus a 5-10% reduction in GI - gross income), 10-20% reduction in GI for maintenance and capital expenditures (major expenses that do not occur every year such as replacing a roof), 10% reduction in GI for property management (if in use), and taxes/insurance/etc. gets us up to the ~50% reduction in GI.

Plan on putting a little aside for major expenditures -- HVAC, new roof, etc.

Utilities, maintenance, capital expenditures, trash, property management, etc.

Once you have that then you can start getting bids from contractors and comps as well as future value appraisal (s)Somehow it will all star to fall into place for you and you will know how to organize yourself and plan our expenditures and do your financial planning as well as your construction schedules. 

"Capital Expenditure".

With enough reserves to cover the mortgage payments for an extended time and any required capital expenditures that may come up.