What you need to understand about data loggers is sample rate. The greater the sample rate the more info you can gather especially when it comes down to monitoring suspension travel for which you need a high sample rate to get the full benefit. If you want it to tune suspension get one with a higher sample rate.

I'm not using g force at the moment but Im sure it could tell you some stuff about how well you car hooks. Shock travel could tell you more about what your suspension is actually doing.

Tailshaft sensor can tell you converter efficiencey/slip % as well as tire spin.

I got my gear from Innovate Motorsports a while back (innovate) from Greg Kelly and he was great to deal and his pricing was the best . You will have a lot of questions about how all this goes together and unless you play with electronics and have a fair idea of how this stuff works you will need some level of support.

Motorsport Innovations

Greg Kelly also sells generic sensors that are much cheaper than the branded stuff. The Racepak sensors are very pricey.