Define your budget.
Select a format 6x4.5, 6x6, 6x7 or 6x9, but be prepared to switch.
Define your primary type of shooting; portraits, landscape, etc.
Define your shooting environment and its needs; studio, on location, walking about, etc.
Will you be carrying it a lot or shooting from a fixed location (studio or near a car)? Bulk and weight are factors when you have to carry the kit any distance.
You said you print your own. What size enlarger do you have? If you have a 6x6 enlarger, are you willing to replace it with a 6x7 enlarger?
Do you need to shoot fast and a lot? That speaks to either a camera with film back to do a quick back change or a 2nd body to switch to.

Personal opinion, if you are going MF, why stop a 6x4.5, go up to 6x6 or 6x7 or all the way up to 6x9 for more negative area. Granted if you crop into a 6x6 you might effectively be printing from a 6x4.5. But as you show in the pix in your post, there are shots that fit a square quite well. It is easier to find 6x7 enlargers than a 6x9 enlarger. Also 6x9 cameras are not very common. I would go with 6x6 or 6x7.

Options are:
- TLR, most are 6x6, most are fixed focal length cameras, so you are stuck with the 75 or 80mm lens. Mamiya has 2 TLRs with interchangeable lenses.
- SLR, 6x4.5 Mamiya, Pentax. 6x6: Hasselblad, Bronica. 6x7: Mamiya RB and RZ, Pentax
- RF 6x4.5: ? . 6x7: Mamiya 7. RF are generally lighter than a SLR. Some have fixed lens, so like the TLR you are stuck with the lens on the camera.
- press, Koni/Omega (I forget the format of this camera)

Even though the spotlight is usually on the SLR, don't overlook the TLR. LOTs of great photos were done with a TLR.

I have not handled a Pentax 6x7, so cannot comment on it.