The TWB size doesn't really matter. In fact, if you look, you'll probably find that it's very small. TWBX files, which are extracted, can be much larger, but that's because they include packaged data extracts. I'd be more concerned about data source or workbook complexity in this situation.
Using a connection to Salesforce with Tableau Online:
my twb info includes:
Size: 1.5MB (largest)
Data Sources: 4 (maximum)
Tabs 30 plus (maximum)
any other comments?
All I'd say is just make sure that you label sheets and comment on fields so that you'll be able to debug and edit the workbook later.
will let you know as I continue to develop and deploy...