after doing a scan said the ABS module is bad and to replace it will cost about N115k, though he said I should still be using the car. readings I have done online suggest that I shouldn't take the warnings lightly.

The only way to deal with the warnings is to take it to a good mechanic/electrician, to carry out a scan/check. Since you have done that already, then go ahead with what he says, except you don't trust him.

There are already 3-4 threads about this same topic...Good though

0rex:

Neutral is safer because utilizing engine braking is subject to the current speed at which the vehicle is moving or a somersault would still occur.
Shifting to Neutral can be safely generalized.

Seconded!

Fulaman198:
Here

Good one...

earthrealm:
you are most likely low on refrigrant, hook up a set of guages and u will see so urself..
then the big question is where is it leaking from...
thats what the techs need to locate, it must b a serious leak for it to go bad just 1 day after refill....
the earlier the beta, u will most likely loose ur lubricating oil , and the compressor will sieze, if you continue driving n topping up refrigrant

seconded...but a comprehensive diagnosis will still be needed though

When to get an oil filter change depends on the condition of your vehicle and driving habits. Since a portion of the engine's oil remains in the filter when the oil is drained, you should change the oil filter at the same time as the oil.