Nice one AL
You wont look back. Good choice .

Just dont strap your shoes to tightly at first or you will start to hurt.

It wont take you long to get used to it.

Watch out for
Pedestrians
Maniacs in cars
Manholes/Grates etc

One thing that takes a bit of learning is the concentration thats required for hours when your riding.
Make sure you spec 2xbottle holders for your drinks. Perhaps a pump holder and small pack to put your innertubes and tyre levers in.

Never replace an innertube without checking your tyre inside for sharp objects. ( everyone does at first then sits at the side of the road ringing a taxi because the fresh innertube has immediatley gone flat)
Always inflate your tyres 120psi
This will make your ride enjoyable/ Nothing worse than riding on part worn tyres.
You will need a good track pump.

Get a helmet/ ensure its not to big and fits correctly.
And bib shorts are a must for comfort.

There are a zillion tips but thats just a few.
If you need info etc. Just ask.
Oh your 12/25 cassete is fairly standard.