I am moving over to DCC because I am not so able to carry out the wiring necessary for a garden railway.

Has anyone any wisdom regarding Garden 00?

The track is 8" off the ground and is decking joists, which have weathered our climate for 6 years now.

My present DC layout appears to be causing problems for our TV reception, especially since we renewed our aerial (Digital).

Does this mean it'll get worse when using DCC locos with their supressors removed? Can I do anythig to lessen the present problem?

keep everything clean is rule number 1 for dc or dcc.
I have used dcc in G scale in the garden with excellent results.
You should not have to remove any supressors to fit chips to locos.
If everything is clean and relatively dry then you should not have any major problems. I have never had an interference problem with dcc.

Place feeds so that a loco is never more than 3 feet from a feed and make sure the wiring is heavy enough for the job and as short as possible. Usual simple test is the coin trick..... Use a coin to short the track, the unit should trip out immediately.

Good luck but it is not really difficult so long as you follow simple rules.