My suggestion is $35 an hour, but, you need to know your capabilities - in order to give a fair value to the customer, you should be able to work at a reasonable speed. Typical rooms like a 20 x 20 size, should cost around - $200 - $300 (around here at least) each to paint...which works out to be around 4 to 5 hours from prep to cleanup. If you know it will take you 8 hours to paint a room of a certain size, but a more experienced painter could do it in 5 or 6, adjust the hourly rate accordingly to be competetive.
When you provide the esitmate, gauge the cost of fuel and do the fuel charge as a flat number...
Labor (expressed as a total number based on measurements)
Fuel charge = flat number to be fair instead of mileage
Materials charge = $5 or so to cover materials like tape, disposable materials
Paint = customer provides or at cost plus delivery charge (buy it from Sherwin Williams and you can get a pro discount after you talk to the manager = you can mark it up to retail for the client).
I've done a lot of painting over the years and this is the basic forumula I use. But, I paint fast and accurately so I charge a slightly higher hourly rate.
As for exterior, to do a good job on a small / medium wood sided house...at least $3000. There's an outfit advertising a whole exterior for $1200...probably a spray job...but I'd question the quality...for what it's worth. Not too many people opting for paint any more - plastic wrap siding is pretty popular.