I don't think lenders will see you as high risk.
If you want to borrow 800k on a 1.5 million valuation that works ot at just over 53% LTV.
You should be able to get 6% interest only on that which works out at approx. 48k PA which is well within your capacity.
The banks will look for details on leases on the properties-If you have 5 years plus that should do it but if you can get longer leases from your tenants now then I would do it.
I presume you mean that your house is worth 800k with only a 77k mortgage.
If you want to PM I can recommend a couple of brokers for you.
I might have a look at paying off the mortgage with the commercial property loan and using your remortgage your house to fund the business instead-this way the funds will be slightly cheaper and will have a little more flexibility.
If the banks are still not happy then I would look at getting a job for a few months to add to your net income-this way they will find it more difficult to turn you down.
There are loads of options out there for financing, I would try to find a good broker instead of going directly to the banks, they should know how to put it together better.
Alternatively look at Anglo Irish or ACC-they are quite good in terms of their risk assessment.
At the end of the day your asset base is strong so if you persevere you will get the money from somewhere.