Hi, i did a event photograph gig recently and am looking for some feedback and advise on my work and gear as im just starting out in this line of work. 

The camera i used is a Canon 850D with 18mm-55mm lens. The settings are shutter speed around 1/100-125, f4-5.6, ISO 2500-6400 for most of the photos.

Here are some of the photos i took. The feedback received from the client was the photos are too dark and not sharp.



Question 1

I read online that I should have use a lens with f2.8 to add more light to the photos. Is it really the issue of my gear? As im just starting out, i dont really have the funds to buy a new lens, is there a work around for this?



Question 2

I also read that i should have used flash when photographing. Won't this annoy the people and event atmosphere?  



Question 3 

For sharpness of the photos, is it caused by the shutter speed? But if i set it higher that 1/125 the photos will turn out to be even darker, how should i approach this issue? I know i can brighten it up in post, but there are 300+ photos, it will take too much time and the client demanded to have the photos the next day.



Would really appreciate some feedback and advise from fellow photographers here, thanks!

Help out a beginner in event photography?