How is the sequencing and how many *different* ways can you sequence on the PSR keyboards?

I've consulted the manual but I can't find the answers I want.

To give you an idea of what I'm looking for,I used to sequence on an Alesis MMT-8 Sequencer,back in the day and it was a joy.You could build patterns(not to be confused with "styles")out of a certain number of measures and work on songs/compositions in small chunks at a time and then go to song mode and string those chunks together to make a complete composition.You could copy and delete measures and even give your "chunks" names so you always knew where you were at.

I'm not expecting the PSR-S900 to follow the same MO as the MMT-8-I just need to know what to expect and see if I could adapt to Yamahas way of working,so to speak.

For the most part,I would build my sequences up without the use of styles and auto accompaniment,like for orchestral/soundtrack work.If I was working on a song,I'd want to be able to use the onboard rhythms(again,without the styles and AA) to cut a rough track and then go back and insert fills and breaks.

I need to find out about this because I don't want to put the 900 on order and then get disappointed with it.This whole bunch of questions would be totally unnecessary if Alesis still made hardware sequencers-I always thought they should revive the MMT-8 as the MMT-16,but I don't think that is ever going to happen.

All answers greatly appreciated!