What would be a suitable aircraft for a short haul freight forwarding business?
You would have to provide more answers to the comment I made above.

But for a relatively small payload (&lt;4000lbs), I'd say you can't go wrong with a Cessna C208 Caravan.  You can buy a good used C208B Super CargoMaster for just shy of $1 million.

Another recommendation for that route would be the DeHavilland DHC-6 Twin Otter.  Payload is increased by 1000 lbs or so over the Caravan and you have the additional safety of two engines for over water operations.  The downside is that these aircraft are fairly prized and will set you back about $ 3-4 million.

Another heavy lifter with an excellent reputation behind it, even after 80 years of service, is the venerable Douglas DC-3/C-47.  You call, we haul 6,000lbs to just about anywhere within fuel range. 

All of these aircraft are extremely rugged and have a good reputation after decades of hard use in bush flying.  They are capable of operating on short, rough airstrips - a good benefit in case you decide to expand to more remote destinations within Cuba and can carry tremendous loads.  They're also turbine powered using PT6 engines (except for the DC-3) so fuel is readily available anywhere in the world as is maintenance and spare parts.