Seconded.

On a): More than a little. Plan to be "90% done" by halfway through the schedule. Remember that "the last 10% takes the other 90% of the time". This is entirely true, and its due to unknowns. When this 90% at halfway approach becomes instinct, you will miss very few deadlines. This has become my internal Golden Rule for non-trivial projects.

On b): My business would never have launched if I didn't constantly stretch my skillset past what I thought I could do. But there is still a limit.

On c): Clients never like unexpected surprises. But they hate them even more if they appear late in the game. Keep expectations in line with reality.