Caltex Havoline is better among all available lubricants
Servis Brand the stock tyre is best for CG no need to change it
You can wash/wax/polish your bike every week nothing harmful but do not use detergents. Buy any good quality of auto shampoo for wash beside this you can follow follow these threads for detailing:
https://www.pakwheels.com/forums/bikes-3-wheelers/200897-my-junoons-pampered-wash-scratch-removal-detailing-pics
https://www.pakwheels.com/forums/bikes-3-wheelers/180526-my-ride-completed-4-years-today
After every 1k tuning has to be done and if possible do change the oil as well
If you want to change stock head light then you have to change the stock beam because it would be melt with the heat of HID so try to find 90 model Honda's beam or else metal beam would cost you around 250-300 use dry battery of 7amp.
https://www.pakwheels.com/forums/bikes-3-wheelers/166142-hid-cg-125-some-other-changes
Nothing to be worry you can ride it continuously would not give any impact on engine