Now i am not an expert on crossbows, just some of my personal input on plearm there:
You have high athletics, low WP in polearm and probably very light armor, since the rest of the gear has high upkeep, so take the longest polearm with high damage ( English Bill is good ) and discipline yourself to stay on its max range
If the enemy instead of attacking, starts back-paddling, in order to trick you into getting to close - you just change to your crossbow for a half a second, and hes after you again
And imo its best to convert that IF to Strength and invest in PS. Or even take shield instead. Iron Flesh makes you die slower, but its better achieved with armor or shield, and as a crossbowman - you are not on "assault squad"