If you want the same channels on the second box you will need a multiroom sub and sky would do this for you.
To DIY install a STB.
You would need to run sat grade cable to the lnb.
You would need to check if you have any spare outputs on the lnb that you currently have.
The lnb is the bit that the cables connect to up on the dish.
Sky prefer this to be one continous cable so not sure about using any points already in place.
As you are getting Sky+ the standard install will be a quad lnb so after using 2 outputs for your sky+ you will have 2 available to use.
Is there any reason why you don't want sky to do this?
KEF 3005SE, Onkyo 606, Panasonic BD30, Panasonic TX-P42V10B, Sky+HD