Doing this will increase the projected annual revenue from approx. $52,000 to $80,000. 

CRA as in Canada Revenue Agency? 

Some areas in SW Florida are showing signs of over saturation, but this investor is showing great revenue and over 90% occupancy.  

If they are so easy to rent, then why are they vacant.If we look at it strictly on a numbers perspective and we assume everything you said was correct, we'd have $93,600 of stabilized revenue.

Property 1: 4/3 LTRCurrent Value: $475kPurchase Price: $363kDown payment: $40k (30 year conventional)Interest Rate: 2.75%Remaining Balance: $294kMortgage payment: $2369AVG revenue: $2775Property 2: Duplex - 3/2 House Airbnb & Detached studio apt 12mo leaseCurrent Value: hopefully within $575k-$600kPurchase Price: $591k (appraised at $599k)Down payment: $30k (30 year FHA)Interest Rate: 6.125%Remaining Balance: $552kMortgage payment: $5041 (including $362 PIM)AVG monthly utilities: $385 (full year avg)AVG monthly revenue: $5261 (full year avg airbnb + $1650/month from apt)

STRs generate about as much hotel tax revenue as the hotels/resorts so there is support at higher levels:  https://poconosvro.wildapricot.org/Economic-ImpactLocal regulation is rough.  74 municipalities each with their own zoning and STR ordinances plus most of the housing stock is in planned communities, many were built as vacation/resort summer homes.  

My clients are going to be fixing up both sides of the duplex, and add another duplex in the back of the lot, for a massive increase in value and revenue in the future.

If they have to go through and segregate the revenue and expenses of each they will generally charge more. 

Consider all of the services a full service short term rental property manager offers: marketing the property on over 50 websites, taking professional listing photos, optimizing rates to maximize revenue, manage all guest interactions from inquiry through checkout, manage all maintenance issues, collect and remit city and state hotel taxes and manage reviews.

@Cody Lewis have you spoke to Mike Savage about his revenue management for STRs?