ok, I get the message

Thanks.
I went for my first double digit ride today, road from Glen Waverley almost to Oakleigh and back again, mostly on the Scotchmans Creek trail. I knew it was there, but had never been near it before - it's really quite nice. The light rain didn't deter, it helped keep things cool.
I've now found my nerve-induced speed limit - 50km. I let the bike get up to that down a larger hill, and though "yup, that's fast enough for me".
So 13km today, in about 1'15". It might sound like a leisurely pace, but I was keeping an eye on the ticker, and I averaged 152bpm, with a peak of 176, I'm not willing to push any harder yet, I've still got some fitness to build.
Definitely must get a bike rack too - the bikes don't fit in the back of the wifes car (she drives the big car) with a passenger in the front seat. I've got a tow bar on order for mine, just have to wait for it to be fabricated and shipped.
Thanks again to everyone - your advice and encouragement is making this a far less daunting experience than it may otherwise have been.