Some areas allow commercially zoned properties to share one large septic system (think sandmound or gravel type system) or would they require an individual on-lot septic? 

If local sales support the new value then you should not have to deal with the seasoning requirement.

We're looking to gather info about likely cost, pitfalls, time required, considerations when obtaining financing, etc. 

- Usually a 5 unit with a boiler means that all the units share the boiler heating system.Which specific utilities in which units are paid by tenants vs shared?

Deduct NEW property taxes after you buyDeduct home insurance costsDeduct maintenance percentage, typically 10%Deduct vacancy+tenant nonperformance percentage(we recommend 5% for Class A, 10% Class B, 20% Class C, good luck with Class D)Deduct whatever dollar/percentage of cashflow you wantNow, what you have left over is the amount for debt service.Enter it into a mortgage calculator, with current interest rate for an investment property, to determine your maximum mortgage amount.Divide the mortgage amount by either 75% or 80%, depending on the required down payment percentage - this is your tentative price to offer.If the property needs repairs, you'll want to deduct 110%-120% of the estimated repairs from this amount.Be sure to also research the ARV and make sure it's 10-20% higher than your tentative purchase price.As long as the ARV checks out, this is the purchase price to offer.It is probably significantly below the asking price.

As always, DYOR (Do Your Own Research) The area has a mix of stable, long-term residents and rental demand—especially with Section 8 tenants—but it does vary block-by-block.Key things to consider are Rental Demand, Property Condition and Management (a local property manager can help navigate tenant screening and city requirements)It’s not as bad as the headlines make it seem, but success here depends on buying right and the right property manager.

It's easy to obtain, costs very little, and doesn't require extra, on-going effort to maintain.

Just finishing the SRT fire inspection requirement's this week. 

there are set requirements for lead generation.

Or start a business which would require a lot more time than owning RE.If it were me and Dallas is appreciating, I'd probably hold onto it since you've had it since 2011.