This will likely have many equations you're interested in:
https://www.nrl.navy.mil/ppd/content/nrl-plasma-formularyI think your linear drift velocity value might be an incomplete picture.
Warburg’s law describes ion drift in a point-to-plane corona discharge and might be a good starting point that looks at the physics of ion drifts in a simple system more amicable to theoretical analysis.
Path length between collisions in a kinetic gas is mostly studied under the term "mean free path" The complete probably density function is a bit more complex though and seems to be fairly recent research. I found two papers which model it to be a logarithmic decay.
Source: Steve T. Paik
Is the mean free path the mean of a distribution? American Journal of Physics 82, 602 (2014)
https://aapt.scitation.org/doi/10.1119/1.4869185Source: Paolo Visco, Frédéric van Wijland, and Emmanuel Trizac
Collisional statistics of the hard-sphere gas Phys. Rev. E 77, 041117 (2008)
https://journals.aps.org/pre/abstract/10.1103/PhysRevE.77.041117Probably density for time between collision is similar and also used to derive path length in the above two papers.
Source: Paolo Visco, Frédéric van Wijland, and Emmanuel Trizac
Collisional statistics of the hard-sphere gas Phys. Rev. E 77, 041117 (2008)
https://journals.aps.org/pre/abstract/10.1103/PhysRevE.77.041117Neither of these studies are for an ionised gas so are probably not 100% accurate for what you're trying to study.
I suggest
also posting your questions to a more physics based forum e.g.
https://www.reddit.com/r/Physics/ You'll likely get better answers for this problem and type of investigation you're undertaking than here which is more an EE forum. Edit: Not to say I dislike your endeavours or you sharing them here but you'll probably get better responses in physics communities than here. If nothing else it seems like a nice vehicle for exploration of ion kinematics.
If you can't get access to the papers PM me.