Hi Yair
1. 有車啦 and 有車
有車啦 usually means, hey , a specific car or bus is coming here. 有車, it could mean so and so has a car or a car has arrived.
2.
What is the difference in Cantonese between 行 and 走?
The first one is for walking, and the second one is for running but they can also mean the same thing.
3.
“佢有錢多過頭”
is this the same as saying:
“佢有錢過頭”
They both mean the same thing. 多 places more emphasis on "more than enough"