I am planning to drive from Rio to Sao Paulo in about a month.

Anyone have any suggestions or advice?

Easy - there is a motorway. Takes ages to get out of and into each city centre though - so I suggest taking air shuttle if at all possible - but then you probably thought of that option already.

Actually, I was planning to take the coast road through Parati.

Has anyone been there?

Your suggestion is through the scenic road. Absolutely amazing but it'll take you a full day (since early in the morning to late in the evening).

You'll just want to stop lots of times. Beautiful beaches and nice spots to have photos !

Great choice !

We drove RIO-Sao Paolo on the coast last year. We made it to Angra-dos-reis, but not to Parati. Its called Costa Verde (Green Coast). A few tips:

1. As metioned it takes forever to get out of RIO and into Sao Paolo City Center. Sao Paolo is probably the worst trafic jam I have seen. It took us about an hour to drive the last 10 miles!! I was told that's just the way it is.
2. The road between RIO and Sao Paolo is good, two lanes each way, gas stations, rest areas, etc. ALL other roads are not very good. Most are one lane each way, some are semi paved roads, pot holes, speed bumps (yes on the roads), horses on the road, people walking as if its a sidewalk, etc..
3. Signage off the main highway is poor and you can easily miss the exits. Usually there is only one sign that may be covered by a tree/vegitation.
4. People are very friendly, but don't speak English or Spanish, only Portugese.
5. A lot of beggars and petty crimes are committed on tourists when in the countryside. People are really poor, no running water, electricity etc.
6. Nice beaches on the way, but nothing special.

If you are driving, I would highly recommend to stay on the main freeway.