I already have a Tank F in two tone and like you, plan to get a YG Love one day.
Personally, I would consider getting the watch pre-owned and the Love new - watches tend to come into the pre-owned market much more readily and in better condition, plus because of their generally more wide-spread availability, the pre-owned prices reflect a greater discount than you typically see for a really top condition second hand Love.
So summary: Love brand new from the Cartier boutique and Tank pre-owned from a reputable reseller (there are plenty out there). And I would get the Love first, avoid another price increase