First Build Questions With Power

Okay, first you will need a full ATX tower, not a mid. If you already have a case that is not a fully tower, don't OC your i5.
Full Towers:
http://www.newegg.com/Product/ProductList.aspx?Submit=E...

Cooler:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Power Supply:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Why on earth would you need a full tower for 2 HDDs and 2 GPUs?

I'd recommend: PC Power and Cooling 750W 80 PLUS SILVER Fully Modular PSU 109.99 also has a $20 MIR.

Also use THIS! link to calculate PSU requirements.

dont overclock without a full tower that is the biggest load of garbage i have ever heard i have never owned a full tower in my life i have overclocked every processor i have had in the last 10 years by any up to 50 % let me see pent d 805 2.66 @ 3.9ghz ,e2160 1.8 @ 3ghz, e5200 2.5 @ 3.8ghz, q9400 2.66@ 3.7ghz and of course 2500k 3.3 @4.5ghz and had plenty of hot gpus and crossfire setups. the i5's arent any hotter than anything else in the past either the 805 was prob the worst for heat. in all that time i have never had my rig overheat or shut down due to heat related issue here in queensland australia where its common for 35c days in summer, aslong as your case is tidy and has sufficient case airflow and you have appropriate cooling and airflow on your cpu and gpu/s you will be fine dont listen to his nonsense!

I was thinking of using the Antec 902 revision3 case as it is quite cheap

Also is modular power worth the extra money, or should I buy a non modular to try to save money?

nice case, modular is good but u should be able to hide excess cables with your case behind your motherboard tray so if you wanna save some cash thats fine. a 'quality' 650 watt psu should be fine something like a seasonic, corsair, high end antec or the likes, try and get a high efficiency one (80+ bronze as a minimum)because the 20% inefficiency turns to heat so the less efficient the more heat

Thanks for the advice, much appreciated