Some of these Airbnb turn overs are every 1-2 days, which means my cleaners are sometimes cleaning the same rental 5 days a week!

I agree with the above advice: Get a professional carpet cleaner and pay them to deep clean, get a handyman to touch up the holes and paint touch up paint and repair/replace the kitchen cabinet door or associated hardware, then get a professional cleaning crew to scrub the kitchen, bathroom and rest of house.

You need to factor in a cleaner for the common areas (kitchen, bathrooms, hallways, living room) once a month.

Should be around 800-1000 (ie 4 hrs ar 120 + 300 transport, or 8 hrs at 100 + 200 transport), more cleaner works.

With the majority of the inherited tenants gone, the place began to look/feel much cleaner however the outside was not on par with the inside.

A savvy renter may know the law better than you and take you to the cleaners.  

You will also have to ensure security deposits are either transferred from the old tenant to the new tenant (i.e. new tenant pays old tenant) or you will need to collect the security deposit from the new tenant and refund the old tenants (minus any valid deductions).We have done it both ways, but the sub-let is likely the easiest for everyone involved as there is no refunding/transfer of individual portions of the security deposit and you have a clean(er) break between the end of one tenancy and the start of the next.

What would be the best route to take then on acquiring more cleaner assets?

Develop working relationships with various service providers such as plumbers, electricians, appliance repair technicians, painters, cleaners etc.  

Looked ok on the outside; but we spent thousands on environmentals (including phase 2), and found PERC as there was a dry cleaner there before.