On board flash

Hey All - I use a d700, but wanted some opinions and C&C please.

I will preface this with "I usually only shoot my kids outside"

My wife's company does corporate events. They were having a team building session in their warehouse at 6 and at about 3:30 they called and asked if I could take some pics. The only flash I have is the on board the d700. I really know nothing about using the flash and didn't have time to review before I set out.
I showed them the pics I took via Ipad and they liked them and even said they wanted a couple for marketing. Anyway, they asked me to shoot an event set up next week. I would like to improve upon my first round so if anyone has tips or C&C of the images below, please share. Also shoot I invest in a flash? How would you shoot an event set up? (The pro photogs are shooting the actual event)

Here are examples:

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Yes, you should invest in a flash. Its an essential part of every photographers kit. Also get yourself a big bounce card like the rogue flashbender or demb flipit.

^^^^^^^^^^^^ Agreed.

Heres what I use to shoot an event. LINKObviously there are less expensive ways, but the general concept remains the same.