As mentioned in the two replies above you don't need to pay anything in
order to see the race. You can use the course map on class1uk.co.uk to
find a spot that is good for you. Obviously the Hoe is popular with
both the Dry Pits and other attractions available. Also it provides a
good view and you can also hear the commentry. Mount Batten is also
popular but if you decide to go there on race day it's better to get
there early as only the end of Mount Batten pier offers good views.
As for the boats you can expect the roar of the Lamborghini V12's and
the American style big block sound of the Mercury V8's.
If you have time available before the practice sessions and / or the
race get down to the wet pits to see the boats being lifted into the
water.
Hope this helps!