I own a 2000 Ninja zzr250 as you can see in my name. I did some residential street practice today. I mostly used first gear which starts revving pretty high at 30km/hr. It revved at like 7-11k (14k is the redline)? Is that detrimental to my bike? No engine wear? What about heat issues? Would it overheat? Usually when I get up that high I should shift right?
For downshifting, my manual says I should downshift at 5k or lower. Is that about right? Or I can do it higher without abusing my bike? If so, I should do it without overrevving the engine or an excessive jump in rpm right?
Running it to redline once in awhile will not harm your bike in the least, as for 7-11k, that's where it should spend most of its life, thats the only place where it makes any power.
High revs without the appropriate speed will eventually cause your engine to overheat. This is because there is not enough airflow over the engine or through the rad.
Just keep an eye on your temp guage if you are worried about overheating.
I see that you have many questions which is alright to ask but may i suggest that you take a refresher or a fast track course from one of the driving schools.
That usually only take one day and you'll get your $$$ worth.
Most people who "outgrow" the 250 never learn how to use it, I suspect you will not be one of them (I think you've asked a good question).
Rev away. Taking it up to the redline on a regular basis will not hurt the engine, but pay attention to how the bike feels, how it pulls. You will notice that there is no extra power (acceleration) beyond a certian point. Sure you keep going faster but there will be a point at which it feels like that is all it is doing.
So the plan would be to take it up (WOT) and just past that point (max pull) and then upshift (if you are wanting max power for a merge or something). You will notice that while the revs will be high you will not be at Max RPM before shifting.
Just riding along in any gear at high RPM is only needed if you figure you want that power on tap.
Extra wear isn't an issue, few bikes are replaced or sold because everything else is perfect but the engine has lower compression or is worn. But you will wear out the bike by always running at WOT and braking hard (like racing). Tire and chain wear will be more noticable than engine wear.
Downshifting can be tricky but you do not have to let the revs drop that much. A training course will help show that you can keep the revs high and up and downshift without hurting the engine.
You can hurt the bike at any RPM but at higher RPM you have more power on tap which means you might do more damage if you screw up a shift.