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Secondary heater is the most important one for a big Dob.
Then the finder, then the other bits like eyepieces etc. Most dob users I know don't have any heating though.
If the primary is generally an inch or thicker it will not usually dew up due to it's thermal mass. It can't radiate heat enough to match the descending fall in ambient temperature during the night. Getting rid of excess heat is more of a problem here. It is not the same as a thin SCT corrector plate.
A shroud may stop the optics radiating heat out into space a little, but once they have reached dewpoint the shroud won't make any difference. The shroud itself can collect dew and drop this on your optics.
I have always just used the Astrosystems Dewguard on my dobs' secondaries, kept the telrad dewshield in place, swapped eyepieces regularly, and kept the fan behind the primary running. Never had a problem.
Heating on the finder, eyepieces and filter slide would be handy though if you're happy with the extra cost and fuss in setting up.
For cooling, fans that scrub the boundary layer off the front of a primary only make a difference if you are wanting to do high-powered viewing in the first few minutes while you are waiting for the mirror to drop in temp. One might help stop dew forming on the front face of a thinner primary though, if the fan behind the mirror was not enough.
If you are going to run a fan all the time, it will move air more efficiently if you seal the bottom of the tube/mirror box, or at least make sure it has a baffle around it. Otherwise lots of air coming out of the front of the fan just circulates round and gets sucked in the back over and over again.
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