hiring everyone he sees for every single thing is kind of stupid. Myths are already passed down, given that king himself explained the reason (which sounds unique to that world), that explanation would spread quite easily. Also problems with a budget.
Being formal with a king establishes a separation with royalty and it's people. Realistically because of informal speech people would start talk disrespectfully with king which would lead to king loosing authority.
You can earn loyalty and respect of your subjects as a king, never as a friend.
Biggest issue is that MC knows everything. rarely you would find a person that could easily construct sever system. Realistically, using logic it would take weeks of work just to understand how it would work from what it does.
Or issue with food. Majority of food that MC shown requires spices, oil that isn't freely available to the masses.
I like to think when reading a manga. It is better than most but when you start to think, you get blinded by massive plot armor that MC has.