The key is start ASAP.   

I cant find out 2 key things: #1 Will it appreciate like a SFH?

I am currently living in the main house, but will soon be moving in the upcoming summer due to another purchase.

if your offer is rejected, move on.hope this helps. 

If you aren't going to move into the property, you will need 20-30% down so you need to factor that in to the price points in your area.I would keep saving instead of activating a low-equity HELOC right now.

It's a medical office building located in Prosper, TX and here's a breakdown of the key details:Property Details:Sale Type: Investment or Owner UserProperty Type: OfficeProperty Subtype: MedicalBuilding Size: 9,657 SFBuilding Class: BYear Built: 2023Percent Leased: 100% (Currently Fully Occupied)Tenancy: Multiple TenantsBuilding Height: 1 StoryLand Acres: 1.00 ACZoning: CommercialFinancials:Purchase Price: $676,000 + $81,000 Tenant Improvement (TI)Down Payment: 20%Commission: $22,000 (agent commission)Monthly Rent: $5,400 + NNN (exact expenses not specified)Vacancy (First 6 Months): Estimated expense of $27,600 (assuming rent starts after 6 months)Mortgage Payment Options:25 year term - $4,000/month15 year term - $4,600/monthLooking for Your Expertise:Does this fully leased medical office building present a good potential investment opportunity?

By maintaining the mortgage on the property, you are taking advantage of one of the key benefits of owning a rental, letting someone else pay your debt. 

I read something called NBT (Net Billing Tariff) may apply but I am unclear how it would impact tenants and if the landlord were to move back into the house after tenants move out?

When we don't find success in a strategy we tend to move to another one. 

We are moving to a rental property in Seattle next month and the lease is already signed.