Argh... I wish there was an option for HL2 style weapon selection!
In HL2, the weapons cycle from the start of the group every time - so, for example, shotgun would always be "3 3 enter" no matter what weapon is selected. Here the weapons cycle from the present location, so the selection for shotgun changes if you have the assault rifle or crossbow active (and similarly for other weapons).
So, instead of just knowing the shortcuts, you need to dynamically adjust the selection based on the weapon you currently have active! The number of times I've selected the crossbow instead of the assault rifle and gotten killed / badly wounded as a result... Maybe it's just that I've played too much HL2 / HL2: DM.