Most loans out there are convention / conforming loans that conform to Fannie Mae / Freddie Mac guidelines.  

In the event of seeking financing through a conventional mortgage in the future, on new large purchases, I’m wondering if we need to disclose the mixed use land contract if we also aren’t disclosing the income from it?

We did a conventional 30yr fixed rate loan. 

We financed the home originally through a conventional loan with a local bank.

You'll have a tough time getting a low-down payment conventional loan that will roll in renovation costs.

Or work differently so you produce a greater income and can buy all cash (or pay down debt so you can get a conventional mortgage)in your question I hear you wanting to be creative, which is awesome - however creative in looking for money means you may want to go where there is money?  

In Canada, generally speaking 2 to 4 units is considered a residential multi-family investment rental property and can be financed with a conventional residential mortgage with 20% down payment with the posted residential market interest rates. 

So I have a rental property which is under a conventional loan but yet it cashflows with the current tenant.

If someone has the credit score, down payment, and debt-to-income ratio that fits conventional standards then they will be able to buy multiple properties personally at once.

You would have to purchase one as an investment property - with conventional a 25% down payment is required for a MFR.