I want to build and refinance to pay back the lender and transition to a traditional mortgage which we then plan to pay off in under 10 years combining our earned income with rental income.

If you are eligible you would just make a Roth contribution, and as @dmitriy notes, there is one combined total contribution limit, so there would be no value to doing both.

@Matthew Bruce BaileyI use what's called a pen, combined with a piece of paper.

It is rare that anyone drops what they are doing to do a showing for us.

IMO raising rents that high rarely happens except when someone wants to evict old tenants and renovate.

I rarely worry why others don’t buy houses.

The big "McDonald's hot coffee" awards you hear about are extremely rare and contain extra punitive damages above and beyond the regular award due to long-term, sustained negligence from the losing party.One other thought to help put your mind at ease: I personally know over 100 real estate investors, and none of them have been sued for more than $5,000. 

Your responsibility if you want to avoid all tax would be to purchase at least $150K using $50K of proceeds.If you want to combine multiple properties it is their aggregate value that will matter. 

This strategy would rarely make sense unless if there was some huge value add factor.

  $ wise, it will be the least expensive (interest rate) to refinance my primary home to a 30 year mortgage, with enough cash out to payoff the rental property.That would change my total combined payment (including taxes and insurance for both properties) to $1300ish, giving me $380 more per month.Dollarwise that makes sense in an instant.