@Heather Spencer I'm not a pro but I dove into the ventilation question a bunch when I was looking at what to do in my own kitchen. There are a ton of posts on it here, too. ventilation is pretty location dependent as far as what you can get away with, but what you should do is use a hood that's sufficient for the range you buy, and provide the makeup air system that's required for it. If you are anywhere that has cold seasons, or if you live in a tight house, you need to have makeup air. Passive systems work in temperate climates, but not so great in cold climates. The makeup air system is designed to prevent a backdraft situation with combustible appliances. In a cold climate with good insulation, houses don't leak, which means your hood vent will suck more air from your house than can be replaced by leaky doors and windows, causing a dangerous situation. The higher the CFM, the harder it is to replace the air without a system in place (gas dryers, gas water heaters, gas fireplaces, and even bath fans contribute to this calc).

For a 48" range you need a serious range hood (Wolf recommends 1100 CFM for their 48" range if I remember correctly). Anything over 400 CFM typically requires makeup air. I ran through the calculations in the code in my state when I was trying to decide on a range and found out that it didn't take much to throw me into full makeup air system, so I decided to go with induction. If you choose a 48" range and pick a lower CFM range hood, you'll end up with smells and smoke, unless you just have the range because it's pretty and don't do more than boil water or make grilled cheese on it. So, in order to do it properly, it costs money. More in cold climates, where makeup air needs to be heated. Less in temperate climates. My builder estimated about $5-6k for the makeup air system (not including hood). I priced out what I would need from fantech, and it got me close to that number. So it is true that the ventilation + hood can be as much if not more than the range itself.

ETA: this isn't specific to 48" ranges - Wolf recommends 500 CFM hoods for their 30" dual fuel range, so it's more about the power of your range than it is about the size of it. But generally the bigger your range, the more power it has.