There's no magic number, but I would want at minimum 6months rent + 10k in liquid/semi liquid funds.

However, you WILL need to liquidate those funds prior to the purchase, and be able to show what the new monthly payment is on the heloc for underwriting, before you can get final loan approval.Be sure you are getting advice from a mortgage professional, not posts from non-LO's. 

So I guess if you want to look at a Balance Sheet and you owe $200k on a property that is worth $300k, ok so you are $100k up, but that's assuming you liquidate that asset..

The cost of capital is higher than a bank and there will still be reasonable liquidity and guarantee requirements. 

Net worth of at least 100% of loan amount, liquidity of 10% of loan amount, multifamily experience etc?

Most of the time keeping liquid cash in your pocket will benefit you the most. 

I have equity in the PA Property plus significant appreciation plus I have an additional 50-60K in liquid assets to throw into a new investment.

That being said... once the step-daughter's role as the Personal Rep is signed off by a judge (from what I've read so far, this takes only 2-3 weeks as long as there is no contest) she can liquidate the assets to satisfy creditors, and as the house is in the foreclosure process, she can liquidate it...

I offer unlimited number of mortgages as long as: your income on the IRS returns qualifies; OR you have 24 months bank statements with deposits in one account to show the income; OR you have plenty of liquid assets as in checking and can make it on asset depletion; OR the subject property can qualify with rents called debt service ratio- rents used are either the actual lease plus deposits or what the appraiser considers the market rents less principle interest tax and HOA. 

That REIT liquidity is a double-edged sword, though.