I was sitting in on a meeting that I didn't need to participate in, so I just drew it up while I listened.
A high pass filter of 80hz is pretty standard for a 6.5" speaker. Some can play a bit lower, down to around 60hz, but that is really pushing it even for really nice 6.5" midbass speakers, and I agree with your original plan to relieve the front speakers of some of the bass. You can realistically play a subwoofer up to about 120hz without having it sound like it's coming from behind you, so a low pass filter for the sub and a high pass filter for the front mids of 80-100hz is usually the sweet spot.
The tweeter high pass filter is a bit trickier sometimes. Playing a tweeter too low can ruin it really quickly. Luckily, the pioneer you ordered has some good options for HPF on the tweeter channels. You can use 2khz, 2.5khz, 3.15khz, 4khz, 5khz, and even higher. A high pass filter of 2k, or 2.5khz would be for really high end tweeters, I wouldn't push those OEM dyns that low at all, if it were me I'd start at 5khz, mute all other speakers, and listen. At moderate volume I'd then bump down to 4khz and listen. You should be able to hear the distortion pretty well, and you'll know that you're playing them too low. Using 24dB slopes all around I would suspect that 3.15khz, or 4khz would work, but I'd need to mess with a set of the actual tweeters to be able to say that with confidence. Having never used them I'm just taking a reasonable guess.
The easiest place to tap into the speaker wires would be at the OEM amp harness. You can use a battery to verify that you have the correct speaker wires, then run some speaker wire from that harness to the outputs of the new amp. I highly recommend using these:
https://www.posi-products.com/posiplug.html
Where is the OEM amp, and where are you putting the new amp? Are you pulling the OEM amp out completely?