Well, I wouldn't say it was the wrong way, just the DOM way ;-)
Firstly DOM functions are not silverstripe - if they don't work then the only place to ask for help in the section UncleCheese moderates - DataObjectManager. For this reason I do not use it - instead I stick close to the core.
Secondly the silverstripe API HasManyComplexTableField & HasOneComplexTableField (which DOM builds on top) are there to use and I have occasionally added one of these - BUT with your dataobjuects set up correctly - then these are scaffolded for you - why write the code again yourself?
I recommend you drop each one of your getCMSFields function from the data objects and see how ModelAdmin scaffolds it all, then change what you want changed...
This totally changes the way i work with SS. I think i finnaly got it...(well...there will be questions in the future ;) )
Now i understand what you mean with adding fields and pushing them to other tabs.
That Modeladmin thing is great...i used everything at once ( DOM and ModelAdmin ), when in fact the modeladmin does it right.
you are very welcome - ModelAdmin was when I started to like silverstripe alot - since I often build web applications the CRUD of data is very important and important to be able to prototype and get something running as soon as possible - write less code get more functionality - thank you silverstripe!
oh and if you want to change the number of results put "$this->setPageSize(15);" in your init (at the end of the dataobject init) - I don't advise putting 999999 into it to show all as this can lead a rather odd looking screen for large numbers of results