The lower peak is a bit slow going at times but it is amazing how rural it feels considering you are in the outskirts of Stockport and Manchester. Stopping at Ashton as Mayalld says is a good idea. Ashton to Castlefield is a days trip, and as said it's well worth spending a couple of days in Manchester. Take the detour over the Barton Tank to Worsley, where it all began and if you are lucky you might get to see the tank swing.
Lymm is one of my favourite stops and the Lymm Brewery Tap is my favourite watering hole, the chippy opposite is good too. There are also a fair number of shops and eateries.
The Red Lion at Moore is also a decent stop and Stockton Heath is good for shops, not forgetting Thorne Marine for any boaty essentials. I reckon about two and a half hours from there to Preston Brook tunnel and you need to be ready to go in to the tunnel between half past and twenty to the hour. It's then roughly two hours between the tunnels to Saltersford Tunnel so you should make the passage two hours from when you went into Preston Brook. Its then about a Hour to Anderton lift.