
If you've got a good propulsion system that's not useful for deceleration,
sure you can use chemical rockets for that part... but even just doing the
deceleration chemically is a major headache.  We're talking seriously high
cruising velocities; taking the velocity down nearly to zero for a Pluto
orbit isn't easy with chemical fuels.

Incidentally, solar sails are not going to be suitable as the acceleration
system for something like this.  They don't go anywhere quickly.  (I speak
as head of mission planning for the Canadian Solar Sail Project, although
that is more or less an honorary title right now because CSSP is dormant.)
They can't fly a mission like this unless you start talking about very
advanced systems that drop in very close to the Sun first.