Cold weather starting problems are not unusual. The easiest way to make it start better is to add an air pre heater. Modern diesel car, boat and truck engines use them if they don't use glow plugs.
Just shop around and find one that fits your air intake reasonably well, then install it and wire it to the starter relay.
then when you push the start button (from inside the cabin?) the intake air will be preheated and the engine will start much quicker. We added one to a Volvo sailboat engine a couple of years ago and it makes all the difference.
As for cold air at the intake, the engine should be able to tolerate the cold air, but you can optimize this by running a portion of the warmed air leaving the engine back into the cool air intake.
I would not restrict the cooling air flow. You need to keep the Mass Air Flow thru the engine at the normal rate. Use a thermometer, like you have been doing to measure cooling air in and out temps to prevent damage.
As the engine gets old and wears out, the compression will get lower and starting will be more difficult. Naturally you will notice it more in cold weather. That's the engine telling you to order a rebuild kit and plan your work.
