Formatting and Partitioning external HDD help please

Hi- still new to iMAC (1TB) and loving it.
I have an external HDD 1.5TB and initiated TimeMachine (seems easy and fit for purpose) to keep a backup of everything on the iMAC

The iMAC did not come with an installation disc – apparently I would need to download the OS again should it fail or corrupt – unfortunately I have a VERY slow net connection – is there any way of backing it up to the external HDD to avoid having to download?
Would cloning sort this issue?
If so – should I put the clone (Using something like CCC) in a separate partition?

Have come across Recovery Agent – does it need to go in a separate partition?

Finally – for now (!!) if I have to create any new partitions on the external HDD will it erase existing files, meaning I have to restart TimeMachine?

As is evident - help is needed needed here please
Many thanks in anticipation

Lion is the first OS that does not ship on a disk. If you have a slow internet connection you can order Lion on a flash drive from Apple for $69. That would be one way....

You mentioned CCC. However, it should be used to clone Lion on a separate external hard drive, not one that you share with Time Machine. CCC will create a bootable clone of your hard drive. It also includes an option to clone the Lion Recovery partition while it's cloning the OS X portion of the hard drive.