Tagalog question: may/meron vs magka-/magkaroon

I'm trying to get a better understanding of when to use these. I think the 3 points below are true. It would be nice if you could correct me if I'm wrong, and/or point out anything else you know that's important when trying to choose.

True or False?

1) May/meron – are negated with wala, can’t show aspect

2) Magka-/magkaroon – are negated with hindi, can show aspect

3) All 4 of these sentences mean “The child has a cold.”

May sipon ang bata.

Merong sipon ang bata.

Nagkakasipon ang bata.

Nagkakaroon ng sipon ang bata.

"May" and "Mayroon" are both used like "has/have". "Meron" is shortened version of "Mayroon". It's what most people use during casual conversations.

May sipon ang bata. = The kid has a cold.

May kotse ako. = I have a car.

Mayroon akong kotse. = I have a car.

Meron akong kotse. = I have a car.

As for "Mag-", it's used for future tense.

Magkakaroon ng sipon ang bata. = The kid will have a cold.

Magkaka-kotse ako. = I will have a car.

Magkakaroon ako ng kotse. = I will have a car.

"Nag-" is for past tense.

Nagkaroon ng sipon ang bata. = The kid had a cold.

Nagkaroon ako ng kotse. = I had a car.

Nagka-kotse ka na ba? = Have you ever had a car?

Tip: We never use "meron" if the prefix is "mag-" or "nag-". It's just used for present tense.