My thoughts from the little I know about the raw numbers however:1) You have no reason to not raise the rent at least a small amount to compensate for the extra cost of ownership the past few years.

Just to give you an example of the type of thing you'd be potentially looking out for, if the community has a pool terrace planned and it's orientation in the new building would face directly towards your property, that could be a source of significant noise and disturbance for you/your tenants, and could make it much harder to sell your property once the new building is built and occupied.On the positive side, new apartment buildings cost millions of dollars to develop and build, and developers really only sink that much money into areas where they're forecasting rent growth and property appreciation for their investment.  

My recommendation would be to own residential first so you have a much better understanding of the costs to own real estate.

This can save you from costly mistakes.

It sounds like you'll have well over $100K into it, between down payment and closing costs - is that accurate?

The rentals are paying the holding costs on it so far (taxes and insurance are high in this market).

Cap rates, location, and understanding the cost per door alongside your mechanicals and capex is going to be key when buying multi-family. 

Oh, let me count the reasons, stark and clear,Why in the Rockies, dreams might disappear.Firstly, time's dance, a tango unforeseen,Delays and setbacks, patience in between.Secondly, budgets shift in mountain air,A treacherous venture, costs rise with care.Like winds that howl, a financial plight,Draining pockets in the mountain's height.Thirdly, expertise, a crucial call,A craft refined to prevent the fall.In rocky realms, build cautiously,For seasoned skill shall guide to victory.Oh, let me count the ways, with wisdom's might,To pause the dream, build in clearer light.Where were you CountTheWaysGPT when I needed you?

I will have access to ~1M in cash for down payment and closing costs (I would also have reserves, separate from this capital).

I’m looking to invest in a property with a partner to split the costs.