Considering traveling nurses/workers, as well as seasonal rental for ND home games (also a huge Fighting Irish family).

I’ve been struggling with no bookings for two months and low view rate, and to top it off, the city just set stricter rules for short-term rentals.

That's their whole game!

I'm looking to build a Casita/poolhouse for use as a short term rental in Summerlin.

Luxury rentals, purchases and short term accommodations will be in high demand from Santa Barbara to San Diego and a drastic uptick in inventory for sale can be anticipated in the areas most effected by the fires. 

Ditto, I use PriceLabs for my STRs - here is a nice writeup ...Airbnb Smart Pricing Vs PriceLabs: An In-Depth Comparison For Hosts | Boost Your Short-Term Rentals

It does eliminate the need to add chlorine but the chlorinators (Pentair IntelliChlor) have a fairly short lifespan.  

If it's on the higher side you may want to consider it for mid-term or long term rental, but if most stays are below 30 it can be viable for short-term! 

So you really need a downpayment + 15k to be in the game.

The only investments I’d do there is in short-term rentals in either Rome, Venice or Florence.