Question Will a USB 3.0 802.11ac 5ghz usb adapter bottleneck with a USB 2.0 port and a 100mpbs connection???

Not likely. The speed you get actually depends on which of many variations of 802.11ac encoding your adapter and router support. It also depends on distance and how your house is made. You might get 100mbps if things are working well. It is not the USB2 that is slowing things down though.

USB2 is rated to 480mbps but with the overhead it is somewhat less but it will come close to keeping up with even the fastest 802.11ac devices. Unless you sit next the router the best device only get 300-350mbps.

But in your case the 100mbps internet connection will likely be the bottleneck.