which RouterBOARD suits LTE USB stick / PCI ?

Hi all,

I’m totally new to the topic and I have a couple of questions regarding connecting a RouterBOARD with LTE perferably using LTE PCIs or usb sticks:

are there specific boards that support LTE ?
is choosing a RouterBOARD here a correct choice ?
does any PCI slot support LTE-PCI given that the chosen PCI is compatible with the software ?
is there any difference between using PCI or USB stick when it comes to connecting the board with LTE?

Many thanks in advance,
Eya