I have recently moved from Pathfinder to DND5e so excuse me for being still confused about the rules.

My Path of the Beast Barbarian got Form of the Beast on third level, and with that, the sweet tail attack (that my master agreed we could pretend to be a tongue because it seemed to me to be much cooler). I have been using the rapier up until this point, because it seems to be fine if I dualclass to rogue at one point for the sneak attack. Of course, the tail (tongue) can not deliver Sneak Attack since it is not a finesse weapon, but it counts as a simple melee weapon for me. So...by what I read in the rules, if i invest in Dual Wielder feet I could use the tail as primary attack and "Dual Wield" the rapier as an-off hand attack. Additionally, the off-hand attack with the rapier could cause a Sneak Attack every round because of Reckless Attack!? Am I following this correctly? Can I even use the shield in the left empty hand?! Does it sound too OP? Can it be house ruled with some limitations?