Hello, good question.
Grease and lubrication is quite controversial depending on who you talk to. Some say don’t line rear bearings. Others say it’s vital…
Ultimately, taking things apart and seeing how they wear is the best indicator of things.
For me, general things I lubricate, loctite, and grease are:
lube: axle bearings (if older or seals gone/compromised), chain, engine driver sprocket (depends on application but usually a bearing grease to pack needle bearings, or if bushing a light application of thin layer of grease), spindles and heim joints. Some karts need lubrication on steering shaft uniball or upright support but these are more rare applications. I take my time on hubs, tend to clean the spindle shaft completely, then apply thin layer of WD40, then tri-flo to bearings and remove excess from both. Make sure to take the time to ensure WD40 is spread across the interface surface of the hub bearings and the spindle, otherwise you can start to see spotting and abnormal wear areas upon hub removal for next service.
I loctite my axle bearing grub screws (aka set screws). You can ignore this if you want, but since doing this I’ve never had one fall out, and I’ve never had an axle move. Some people are horrified at the concept of doing something like this, but to me I reeeeaaallly don’t want that axle to move laterally in the kart. I also loctite certain engine related hardware such as the retaining bolt for the clutch on a Briggs, or vibration-prone hardware, but this is somewhat dependent on what engine is run.
I’ve never used T-9, but based on what it looks like it is as a product likely you don’t need it much of anywhere. If you are careful and keep it away from the brake system you could lightly coat the axle with it as it is bare metal…