On cold mornings it can take quite a while to get warm oil into the waste-gate mechanism so sometimes that can make it a bit sluggish to close and therefore slow to bring on the boost. Expect some lag, pause on increasing the throttle position once you get just over 30" to allow the turbo to spool up then feed in the remainder smoothly.
If you're sticking to 500fpm RoD, then 6nm/1000ft may work out well for descent planning; especially if you have to advise ATC as they will typically only allow for 3nm/1000ft.
For any given fixed manifold pressure, boost will be higher as you climb, lower as you descend... so that 25" at 10,000ft boost should be around 6"; at 1000ft 25" should be producing no boost at all (therefore a coolish turbo).
Sea level manifold pressure is around 30" less 1.5" for engine inefficiencies (e.g. air filter, throttle turbulence) so its typically around 28.5".
Then, you will need about 1" of boost per 1000ft on climb to maintain the same manifold pressure.
Be mindful that traffic in the flight levels will typically be TAS'ing around 240kts+
Watch out for the EGT, keep it within limits, especially on descent.
Don't slam the mixture full rich at ToD, or shock cooling can result.
If you're on the Oxy be mindful that it is at zero (or close to it) humidity, so STAY HYDRATED! Hypoxia is induced earlier when dehydrated. Get familiar with the symptoms of hypoxia and don't muck around with it. If more than one pilot/pax is using oxy, make sure you use an antiseptic wipe on the nasal cannular tubes so that you don't catch anyone else's cold.
Descending from flight levels with a cold might leave you with barotrauma so don't try it.
Have a look through the performance section of the manual and run a few basic calculations to compare time, fuel & distance to climb vs TAS and Groundspeed so that you end up at select the most efficient level you can.. i.e. not at FL220 for a 30nm sector and not at 3000 for a 120nm sector.
Good luck, enjoy it!
TSIO540