Nowadays motherboards start to have more USB 3.0 ports than USB 2.0 ports, which is a problem. Windows 7 does not come with USB 3.0 drivers. As a result, I cannot install Windows 7 from a USB flash drive on a USB 3.0 port. I ran into this problem when installing Windows 7 with ASUS Q87T/CSM, which only has USB 3.0 ports.
Some motherboards retain USB 2.0 ports but only two of those. That might still be a problem. Presumably you would have a USB mouse and a USB keyboard, which consumes two USB 2.0 ports. Where do you plug in the installation flash drive? I suppose a USB 2.0 hub will solve the problem, although I have not test it myself.
You might get two additional USB ports on the case front panel, but whether you can use them again depends on the motherboard. Pretty much all motherboards have internal USB 2.0 connectors, but not necessarily internal USB 3.0. Recall Windows 7 does not support USB 3.0 out of the box. If the front panel has USB 3.0 ports, the simplest solution is an internal 19-pin to 9-pin adapter. But it is not something that everyone keeps in his toolbox. Some cases come with one, e.g. Lian Li; others do not. So, it might be a good idea to keep one of those adapters around. Alternatively, you could also use a 9-pin to USB Type A adapter (the link is a 4-pin, but same idea).
Presumably this will no longer be a problem with Windows 10. Let’s just hope that Windows 10 is not another Windows 8/8.1.