Your life circumstances heavily influence your appetite for risk and where the money should be allocated.  

As long as you purchase at least $500K ish and use all $140K ish in the purchases you'll defer all tax.And you can allocate the proceeds in any way you want. 

Look for several replacement properties and allocate that 800K in whatever way you want to get to 1.3 of purchase.  

given its asset allocation of some sort (rei), then opportunity cost would be a consideration.So currently 12% is "good"

The splits and allocations thereafter will range based on your track record, experience, how "juicy" your deal is, risk, team, hold period, and other factors.Good luck!!

When house hacking, you need to allocate expenses and income based on the portion of your home used for rental purposes versus personal use.

I was originally planning to put all my monthly returns to pay down the HELOC as quickly as possible so that I can get into the next property but am worried about how to deal with paying the taxes if I don't allocate any of the returns to the side.

Balancing both goals can be achieved through a hybrid approach, where a portion of funds is allocated towards paying down the primary residence while also saving or investing in another property.

Great options if you are looking for full-blown property management options.If you have multiple rentals you'll need the version of Quickbooks Online with "classes" ($85 per month to @Simon W. point) to allocate the income and expenses between different properties and their chart of accounts (list of income and expense types) doesn't come setup out of the box for real estate.For real estate-focused "accounting & tax software" I'd recommend Stessa (Free to start) and Digb.com ($1 a month to start) and Quicken is also a cheap option like @Bill Brandt mention.

I do not have a very urgent need to sell, simply I want to allocate the money to some other assets.