Yes you can record direct by USB. I'm guessing where the manual refers to XLR it is talking about the routing of the audio and letting you know the audio that is sent by USB is routed from the XLR outputs, this is significant as in most cases the setup on the 1/4 outputs is slightly different to the XLR outputs so that it is possible to have cab modeling to FOH and no cab modeling and an optimised signal going to your rig.
You do not need an interface, the GSP1101 is a recording interface.
For the purpose of recording guitar I see no benefit in using a separate interface.
I have not experienced latency issues, YMMV.
You do not need an interface, the GSP1101 is a recording interface.
For the purpose of recording guitar I see no benefit in using a separate interface.
I have not experienced latency issues, YMMV.