Connecting 240 volt generator to Main Panel
The floating neutral is good news, but you don't need a ground rod for this

The fact that your generator has a floating neutral is actually quite fortunate for you, as breaker-interlock-based transfer setups are largely incompatible with generators that have bonded neutrals (the more common case).  However, since you're plugging your generator into your house, which already has a grounding electrode system (ground rods, etc), you don't need to add a ground rod at the generator, as the house supplies both the grounding electrodes and the neutral-to-ground bond point.

As to the inlet, since it's your main panel, you can land both wires on the same bar

A common "shortcut" in main panels (esp. in residential work) is to slobber all the neutrals and grounds onto the same bar, since that's where neutral and ground meet.  Since most panels where this is done don't have separate ground bars fitted to begin with, you're left with little choice but to continue this practice, unless you wish to buy a ground bar kit for your specific make and model of panel and add a separate ground bar.