You only need all that and put a hole in the tank for 3 kW elements 2 kW elements are available but check with a sparky that your electricity is upto it.
Really doing it on a budget you can get 1kw and 1.5kw "travel" elements for boiling water in a bucket, I used these for a couple of years simply unscrew your tank lid and throw it in, (set it in the tank about an inch from the bottom) not as powerful as the immersion elements but I used to get 30degrees in a 500 litre tank when it was minus 3 and that was running from midnight to 7 am
Used to get them off eBay for about £8 - make sure they have the 3 pin plug tho
Darran