Webasto diesel combo water/air heater or a separate system with Webasto diesel air heater and Isotemp? And which diesel heater should I get?

Hey guys,

I am going a little mental trying to plan the components for my Ford Transit. Coming here for some desperate help, as a complete newbie who don't want to mess up. After some research I was intrigued by the Isotemp Slim Square 16l water heating system, and decided on this one. After this I went on to find out which diesel heater I wanted (2kw or 5kw). I then found out that Webasto has a combi system that also heats up water. My brain stopped braining at that moment so I come to you for guidance.

My following questions are:
- How does this diesel combo heater for air/water work, why is it better than the isotemp/why not? Anyone with experience here?
- For those with the Isotemp: What's your experience so far? Would you install it again if you got a new van?
- What Webasto diesel heater should I get? The 2kw or the 5kw?

Some info that may be relevant:
- I will mostly stay in extremely cold areas as I live far up north, but I also go south whenever I get the chance.
- I am also installing a Cubic Mini Wood Stove in addition to the diesel heater.
- It is not the biggest Transit (med. roof, LWB not extended), so I also have to consider the sizes of everything installed + that the area to warm up is small.
- I won't travel a lot to high altitudes, in the rare occasion I will use my wood stove.
- I do not worry that much about the budget for my heating systems as I want the absolute best for full time living in a van in very cold weather.

Sorry for being the new pain in the ass in this group, I am sure this has been discussed before but I am struggling to find good answers.

Thank you so much <3