Yes the procedure for take-off is subtly different from that for the landing in 12-I.
Perhaps it assumes worst case that the aircraft has been shut down and restarted on the helideck and is a more thorough check that the SOVs are opening and closing correctly.
That is exactly right mate
AFAIK. The only way to be sure the air bleed for the heater is closed is to look for the ITT drop when you switch the heater off. That may mean switching it on then switching it straight back off. Obviously, it is difficult to miss the heater being on under normal circumstances, however, doors open, lots of air/noise, you could miss it. I have actually had a couple of heaters stuck on (after a service!!!!) here in the sandbox. Hard to miss here due to the extreme whining noise from the rear crew.