I Did, only much higher than 3 feet so my answer is yes. Just remember you'll need a coupling and straps to secure the pipe. Good luck.
It depends on how long a span you want. 10 foot yes
Patrick: I've bought a lot of EMT and electrical supplies from HD and I've never heard of a 20% discount or any discount for that matter. If you believe there is a discount to be had then I'd suggest that you start with the PRO desk and ask about the discount in person. If no luck then I'd go to the customer service desk and request to speak with the Electrical Dept. manager. Good lock.
TTTT: The product page at homedepot.com states that it is galvanized steel with a zinc coating. There is no mention of lead anywhere on their page. I cannot imagine that lead would be used in any EMT sold by HD. As for the Prop65, you'll have to ask them in the store in the electrical dept. Good luck.
Inside dimension is 3/4. Word of advice, don't forget when you put wires in conduit it raises the temperature of the wires as they are now encased so don't jam as many wires as possible thru it, leave some breathing room.
If you mean pipe clamps to mount the pipe then check out the HD pipe fittings area, they should have everything you need.
Not usually (that I know of). Most people buy a 5 or 10 foot length and cut it to size using a hack saw..
Yes! To any length you need.