airport extreme

My question is, will this disable the wifi on the modem/router and remove it from being a possible access point?

If you set up the modem/router to work in Bridge Mode, then it will very likely function only as a simple modem.....with no WiFi function.

Might be a good idea to check with your ISP before you try this, to find out 1) Whether it is even possible to set up the modem/router to function only as a simple modem, and 2) whether they will support this type of setup.

One option you might consider would be to set up your existing products to function as a "roaming network". To do that, you would change the name of the wireless network and password one of your access points to match the name and password on the other. In theory, you will have one "big" wireless network this way, so you won't have to switch networks when the location of a wireless device changes from one area near one access point to another area near the other access point.

In practice though, some devices may not automatically switch from one access point to another as they move about the house, so if you are interested in the "roaming" concept, you may have to try it out to see how it works for you.

why doesn't putting the airport extreme in bridge mode in my set up disable wifi?

Because the AirPort Extreme is not a modem/router....it has no modem on board at all.....and when you place a modem/router in Bridge Mode, you are making it a simple modem.

In other words, Bridge Mode has different meanings depending on what type of device will be set up in "bridge".

in most cases if you put the modem/router connected directly to the internet in bridge mode it will disable wifi and it can't be used as an access point.

Correct

Now, if you wanted to purchase a separate modem only.....(it will have only one Ethernet port), then you could likely make the AirPort Extreme your "main" router......and depending on the capabilities of the modem/router.....you might be able to make it act like a second wireless access point.

I can't recall seeing a modem/router that could be set up to act only as a wireless access point....but they might exist. Check with your ISP to find out if your modem/router has that type of capability. Odds are, it won't.