Are these all OK?
You sit in front of the computer all day.
Your debt is nothing compared to mine.
I had a similar experience like that once.
Don't compare what you do with what I do.
I was coming out of the house when he came.

Question

Answer

Yes, they are all fine grammatically. The last one is stylistically awkward because it uses the verb 'come'  twice, which is ugly, especially as the two uses of it here have opposite meanings (leaving/arriving). I would change one or other of them: I was just going out when he came, or I was just coming out when he arrived.

Answer

Mostly, yes.

For the last one, it would be preferable to say "I was coming out of the house when he ARRIVED" or "I was coming out of the house when he CAME HOME."