Yeah, that is why Mesh networks are becoming so popular.
As a crow flies it would be 50 ft from the router
With your house being three stories, I suspect 50 feet is still an extreme over-estimate. My house is a 2200sq foot "raised ranch" - that is, two stories with the main level on top. And the house only measures about 45 feet wide by 25 feet deep. So 50 feet from anywhere in the house would put me outside in the cold!
So with my house being just two stories, it has a larger "footprint" on my lot which means the distance from one end to the other is more than yours - since your house has 3 stories and is not quite as big. Your house is surely taller, but not as wide. But even so, typical walls are 8 feet tall. And typical floors are about 12 inches thick. So unless you have 20 foot ceilings, each level on your home is probably around 9 - 10 feet tall.
My modem and wireless router (also 11ac) are located on a shelf, in the middle of the top floor. I have no problem with wireless access anywhere, including the furthest distances in the lower level - which involve one floor and 3 walls.
So again, if you can move your WAP (wireless access point - typically integrated with a wireless router or gateway) to a central location in the middle of the house on the 2nd floor, that might solve all your problems without having to buy anything new. This is especially true since you already have an 11ac device which should give you plenty of range - at least on the 2.4GHz band.
If you do end up buying new network equipment, I would start with just the new router and see if that resolves your problem. Unless you have very thick, concrete walls and floors/ceilings, you should not need an extender. And unless you still have a bunch of kids in the house - all hogging bandwidth with their own devices - I would not worry about bandwidth either.
It is also important to note that communications is a two-way street. Very often the problem is not the WAP, but the network adapter on the distant computer or other wireless device. Often, just switching to something like this adapter can cure all.
BTW, since you live in the US, you might want to check your Verizon contract. Typically you do not have to buy (or rent) your network equipment from your provider. You can buy your own from another retailer - which is what I do. If you rent the device, you end up paying for it over and over again in rental fees. If you buy from them, you typically pay more than what you would from Amazon, Walmart or Best Buy. Most ISPs maintain a list of compatible devices.
That said, if you do get it from them, they provide the tech support. So do what you are most comfortable with.
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