Hi tp,
I have experience of a holiday home with a remote CCTV system somewhere in the UK sticks.
It had a direct exchange line (ie no street cabinets) with a 512k down and 384k up ADSL connection.
I was recommended a Bipac Billion router as this gives fine grained control over the signal to Noise settings to allow you to get the best out of your line.
I used zoneminder running on a linux box to run 4 cameras, through a 4 port AV card.
From my experience I would recommend:
1. Get a business rate tariff with a fixed IP as it will make logging in much easier and you are likely to get slightly less contentions so a bit better performance;
2. You need to think about UPS for both the system and the router for the day when the alarm goes off because the power has failed;
3. You need to think about remote reboot because some day the system will freeze at the least convenient moment and you will need to reboot either the system or the router.
HTH
EG