I’ll try and do as many as I can get done, whilst maintaining a work-life balance and sanity or before I lose the motivation/have my soul destroyed by rejections.
I would really suggest doing more than 5-6, unless you’ve highly targeted firms and there are only that many which specialise in a particular practice/country. Or for whatever reason you are really limited by time constraints.
I think some people that suggest doing a select few don’t appreciate the harsh realities of the process. I say this having personally been victim to such advice.
Quality and quantity are not mutually exclusive!!!!
Don’t aim for a number. Research firms, the type of work you’re interested and apply.
In the end I think time constraints for us all (uni/work/life/time it takes to complete an application/etc) make us arrive at a number and that number is different for each of us depending on our circumstances.