Every-time I mess with the worldgen parameters, Either i get endless rejected worlds and nothing is made, or it takes nearly an HOUR to create the world... and then crashes :/
All I want is a large world with huge mountains, lots of valleys, volcanos and lots of map ares with a height of 80Z levels or so :/
What am I doing wrong?
Typically the first thing I do when generating a custom world is to go through all the "Minimum number of xxxxx squares" settings (at the bottom of the list) and set them all to null. This is typically the number one cause of large numbers of rejects. These numbers are tuned to generate a nice, balanced world. If you're mucking around with the worldgen params, chances are you don't want, and won't get, a nice balanced world. So setting these to null is a good idea. Also you might want to set "minimum edge oceans" to null if you are doing anything that might prevent the map from generating oceans. It may also be necessary to go through the "Minimum Initial xxxx Square Count" and "Region Count" settings and nullify some or all of them as well if you are generating a very extreme world.
Oh, and note that I think you're misunderstanding "Minimum Volcanos"... you can't simply increase "Minimum Volcanos" and hope the map will randomly generate enough. That's simply a reject setting. If it doesn't reach the minimum number of volcanos it will try again, with the same settings. This is probably why it's going into an endless reject loop. If you want more volcanos, you need to change the volcanism properties.
Once you've done that, you should only get minimal map rejects. If this doesn't solve the rejects problem, make sure you edit your init.txt to set LOG_MAP_REJECTS to YES. This will create a map_rejection_log.txt that tells you where the worldgen is failing and should point you in the right direction of fixing it.
NOW, to create the volcanos you want, the best way I've found is to mess around with the mesh-size and weighted range settings. I believe that a Volcanism of 100 results in a volcano, so you're going to want to set the volcanism 80-100 range to something high, try 10 to start. You also MUST set a volcanism mesh size for the weighted ranges to work, not exactly sure what this does, but 4x4 and 8x8 seem to work fine for me. I usually add a high value to 0-20 or 20-40 volcanism as well -- if your volcanism is too high, you will have a lot of difficulty finding any sedimentary layers and all the goodies that come in them.
I'm not quite sure what the "Min and Max Z-level" settings you're referring to... The best way to get lots of z-levels is to again use the weighted range, this time for elevation. I like to set 60-80 to 5, 80-100 to 5, and either 0-20 or 20-40 to 5. this should create lots of mountains, and occasionally deep valleys and some low plateaus. You can also try playing with the "Z-levels above layer xxxx" settings but I haven't had much success with that. Elevation is still the best in my opinion. You can also try pumping up the Elevation and Volcanism Variances... this should make it rapidly transition between high and low volcanism/elevation in a shorter area, making those valleys you want and giving you a better chance of finding sedimentary near a volcano.
Also, if you're having performance issues, I'd create a smaller map unless you desperately need a large one for some reason. Pocket-size maps should generate very quickly regardless of settings.
Hope that helps.