First of all Halo2 is just a benefits add on, it is not a technology.
It is not clear from your post how your new service is going to be provided, i.e whether you are moving to full fibre or not.
Assuming you are not moving to full fibre, if you do decide to take the package, you can either keep your existing setup with modem and Hub3 or if you do decide to use the Smart hub 2 it will be plug and play. The modem will no longer be needed, you just unplug the lead from the DSL socket on the modem and plug it in the DSL socket on the SH2.
If you are moving to full fibre, it will require an engineer to install the fibre ONT (fibre modem) to replace your current modem.