Not sure about number of usb available, but have fully tested a 2700x on Asus Prime B450M-A with 3 types of cooling.
The board is capable of holding a boosted clock of 4ghz and is mostly reliant on cooling more so than anything else. Has 6 usb ports on the rear, couple of plugs for front panel and a pcie 1x slot for a usb card.
Ive had the board for a few months now and have tested 4 processors with it. Its a pretty solid board for being lower end.