Just looked at their website and they state that infants heavier than 10kg or over 10 months may not use a bassinet so i guess unless you plan on buying a seat you'll have your son on your lap, you may want to plan on buying him his own seat if he is really that heavy specially considering how long the flights are

I wouldn't imagine you'd have any problem taking an average sized stroller, depends how bulky it is i guess but i can't find anything on etihad's website