Most likely the screened in porch isnt built to have a room put over it, so that would have to be torn down, and a new foundation installed and then the screen room rebuilt, so very easily could get very expensive.

I have about $100-125k total to spend on renovations to the house but that includes opening up the kitchen/dining room/living room area and completely updating the kitchen.

Given that information, no, your budget won’t cover all of the work you want done.

Would I need closer to $150k? 200k?

Just opening up your living space is a wild card if you end up doing major structural changes. I don’t think anyone can predict the cost of all you want to do, but most will agree that your budget it way too low to accomplish everything on your list. And this is also impacted by living in a high/low cost of living area, age of your home, etc etc.

Opening up the living space/updating the kitchen was estimated at $40k for another couple we know who was interested in buying this house before we did. It's been done to most of the split levels in this neighborhood and seems fairly straightforward.

Your entire budget could easily be consumed by just the addition . Something will have to give. More money or less projects.. We have no idea how large your kitchen is or the scope. 20k-50k+++++.New flooring throughout kitchen and new addition? I mean... you can see where I’m going with this. Get your quotes... you’ll get a far more accurate answer than from people like me guessing with not much information to go on.