Darren,
To answer your question, I don't have a drilling machine, all mine is done with the mill.
It just takes a lot longer than it would with a drilling machine.
ISO 30 is a standard used in industry, and I think you will be hard pushed to find the tooling at the same sort of prices you will find for our general use of MT or R8.
Your thought of using adapters to use your original tooling defeats the object of moving to a larger more rigid precision machine. As soon as you use an adapter, precision and rigidity tend to go out of the door. They should only be used in a dire emergency to get yourself out of a fix, not to convert a machine from one standard to another. But it is up to you whether you go that route.
When I bought my machine, I also considered this one
http://www.chesteruk.net/store/model_t_universal.htmIt was great because it had a horizontal spindle as well, but I soon realised that my toolholding and tooling costs would triple instantly because of the industry standard tool fitting. So that choice was rejected
If you want to take the plunge and go down that route, you might be able to reduce the cost by searching for industrial machine and tooling auctions, rather than the hobby tooling distributors.
If you want to use adapter sleeves, then Chester do them on this page under the sleeves heading
http://www.chesteruk.net/store/tool_holding.htmI hope that this has helped.
John