Vacancy will depend on the product you are providing, the market demand for that product in the specific area your property is located, the market, how you price your units etc...For example I own one duplex since 1993 that has a vacancy rate of less than 1% and I own a 9 unit bldg since 2008 that is 10%

I would go into the renovation thinking about the final product as a rental and how to get the most of that future investment, and less about what you want now. 

Is this a unique mortgage product only for physicians?

At the end of the day, we send a follow-up email to the team where we score our productivity for the day on a scale of 1-10 and list the tasks completed.

A lot of forum members are very knowledgeable in their respective fields related to real estate investing, whether that is real estate sales, wholesaling, flipping, rentals, lending, self-directed IRA and Solo 401k investing, or tax and legal guidance.Discounts on some products and services are offered to BP members: https://www.biggerpockets.com/perks/proIf you haven’t been to it already, you might want to check out the BP blog: https://www.biggerpockets.com/blog/The site has quite a few tools that can be helpful for new members.

Yes, they will be using your personal credit score and, depending on your loan product, will use a debt-to-income ratio analysis (includes your personal finances) or perhaps the property deal itself (doesn't matter what income you personally make) to determine how much they will loan you.

How are people staying productive at this time, particularly in terms of acquisitions? 

Especially when starting out because you only pay interest if you are currently barrowing and only on that amount.To be clear, a HELOC (line of credit) and a HEL (fixed payment loan) are two different products with different benefits.To use a HELOC as funding for investment property can be a great tool and is one I have used a few times.

Yes, most lenders offer refi products, but you'll want to find one that works with investors and has investor friendly products. 

Also, working with a broker who specializes in working with investors will benefit you greatly as they will have advanced knowledge of coverage's/products available/relationships with their company representatives.