No of speakers/power to cover room of 500 people?

Rule of thumb is about 10W per person.
So for 500 people that is 5000W or 5 kW.
You deliver (steady) about 700 W so this means you will be about 4300 W short.

This is for indoors. If you play OpenAir I like to have double of the above.

This is why I only rent PAs from a local sound crew, as it would be much to expensive to have a PA for anything larger than 200 people by yourself and keep it up to date and scalable. (Large Scale PAs are stackable in stacks of 500 to 1000 W that you put on top of each other and most of the time need special equipment to get in the air, as normal stands wont cut it anymore)

I think 5000 watts is still a little short for something of the scale.

We did a show @ a large venue…it was for DubFX and the venue capacity was 1400 and we had about 1200 in the place…and we used a total of 40,000 Watts….and that was a bit much…30k would have sufficed…

I think this largely also depends on the size and shape of the venue too. IMO anything over 300 ppls in a big room should have at LEAST 10k, as well the genre of music is a big factor too.

You are of course right Hee, having more headroom in wattage is always good.
I use the above rule as a “rule of thumb” for absolute minimum level. So if anyone asks me this is the absolute minimum I would play over.
If I can decide myself or use the soundcrew I usually hire when they leave it in my hands, it is at least double or triple that even if we do not need it, it is always better to have reserves as you mentioned. Having your 40k was prolly a good thing, even if you did not need it. I find if you bring a little over the top and just do not crank it to the end, you get even better dynamics in the room/venue and can be more flexible with speaker placement.