Hi again.
It's correct that the graphical table editor doesn't provide the option to create columns for all data types.
As this tool is mainly meant to serve monitoring and checking purposes.
To actually develop tables, you're better off to write the create table script as DDL (and put it into your version management of choice).
And with that you can just go on and create TEXT columns.
Concerning the "is the merge necessary" question:
The short answer is: yes, it is.
The full - for now - answer is:
Since the connections between the column values that belong to one specific row is done via offsets, all columns of a table must be processed during a merge/compression-optimization run.
Otherwise the sort order of the leading column could change and then the rows couldn't be put together again correctly.
I'm not going to do byte-counting on internal structures for which the exact implementation is not released to public here 
.
Finally: although understandable, but ignoring the possibility for an undersized system is not the best choice. We've already seen customers struggling with memory/cpu issues that in fact were caused by "too much data for this setup".
- Lars