Okay, an '87- puts us in the same boat. I have an '87 300D with the same exact engine. 2K rpm isn't too high at all, it's still short. These engines are noisy and it's something you have to get used to. I don't beat my poor car to the death but I'll rev her to 4K rpm without manually shifting, just taking off "in a hurry" every once in a while, it it's perfectly fine
It can actually be beneficial to get the car up in those higher RPM's, it blows carbon out of the engine and exhaust, and keeps your car purrrrring. Really though, you wont have any problems opporating your engine at any rpm under 5000.
And for your other question.. these car's have odd power bands, making it hard to say what rpm would be "ideal". If it gets you from point A to B and it's under 5000 rpm, then you're allll good