Sitting isn’t the best for them. If you can run it, run it! Some of the issues can be rust in the turbo, oil getting nasty, if outside, you don’t want your oil pan sitting around in the weeds long.
Oil – feel free to run 5/40 Synthetic year round. Some people will say it is too thin – run away quick, they know nothing about oil! At operating temp, it is the same weight as 15/40. I send my 5/40 to the lab ever 5/6k – I have the same amount of shear as motorcraft 15/40. Youre all good year round with synthetic 5/40. I would only run motorcraft, or international filters on your truck. Dieselfiltersonline has them cheap.
For the fuel filters…. Really depends. I get my fuel from a station that has a lot of traffic. The fuel is clean and free of water. I change every 15k. Now If I was filling up from a pump that is sketchy or from the back of a construction truck, I would do it sooner.
Intake – only way to go is the DIY intake. I never did one on my 7.3 but should.
Winter operation – anti gel is good. Opti Lube makes one heck of a product. Cetane, anti gel, and lube increase. Great stuff! Plug it in for 4 hours or so. The sweet spot for all these international motors is right around 4/5 hours. Anything more is a waste. Example = my truck will be at 110* coolant temp when plugged in for 4 hours in 18* weather. When plugged in for 7 hours, coolant is at 110*
You have a diesel truck….drive it, love it, use it, flex its muscles often.
As far as donts. Dont freak out if it isnt running right..... Its a 7.3 More than likley the issue will end up being bad fuel or an ICP!