We will need a lot more info. Bedrooms need bathrooms so #4 does not really have one. How many bedrooms do you NEED I hate bonus rooms you either have a use or don't have one . You will need an engineer to tell you what walls are structural and hold up the house and wich can easiliy be moved. TYpical 60s ranch which I usually like for layout . Why a den and an office ? The kitchen is awful and needs to be bigger IMO so that would be my first consideration. Once you come back with your needs then we will need a to scale floor plan with every measurement clearly marked . You do know modern farmhouse is not something to aim for. A home needs first to suit your life . So if at all possible find out what you can do with the structure within your budget for sure that is where you sart

This sounds like a very ambitious project--you should probably contact a good architect.

I’d consider re-doing the kitchen and opening it up to the dining room for a more open, casual feel. I would put in consistent engineered wood flooring throughout the whole house and paint the main rooms a more relaxing neutral

Get in a structural pro. You have a lot of pillars. It might be because those are structurally necessary. I know you say more open, but what do you want to accomplish? Do you need your counter/cabinet space in the kitchen, or willing to give some of it up to open it up? Or might you need more kitchen space, and willing to give up some dining room to do it? How do you use the house, how many people- do you entertain much or no? Might you need outdoor access to gardens or the like that you need garden processing added in?

If you have a good amount of money for the make over, "good on ya".

A blog for you.

https://farmhouseliving.com/blog/1960s-ranch-renovation-home-tour/