Speakers are a personal choice. Find a shop and listen to them. From my perspective, Pioneer is not traditionally known as a good speaker company. JL, Focal are more logical choice for subs.
Because you have a B&O system, you are in a bit of a spot. Especially when it comes to adding a sub. The B&O systems has crazy aggressive bass management in place to keep Ford from having blown speakers come in for warranty work all the time. So as you turn the volume up, the bass goes down.
These means you really have no place to take a signal for the sub. And high level inputs are bad anyway.
So you are forced with the B&O system to use the ZEN A2B device that plugs into the factory can bus. The good news is, it is all digital, no signal processing at all. so you defeat the bass management.
The bad news is, you have to remove the stock amp, which means your mono amp will not be enough, you need an additional 4 channel amp for the front and rear doors, and at minimum you need to replace the speakers in the front doors and tweeters in the a pillars. You could leave the rear doors stock, but why at this point.
With the B&O system, you are looking at replacing it all, or dont do it scenario, which makes the price to play start at around $2,000+ IF you know how to do it yourself. $3,000+ if you have to pay someone to do it for you.