The boat was launched at Titchmarsh Marine, who were very helpful. Also at a reasonable cost. The slipway can be used at all states of the tide and I did watch a boat being launched at low tide. However, there was a thin layer of mud on the lower part and unless you are desperate, it may be worth waiting for about half tide before recovering a boat.
Access to the slip is only available during office hours, when the harbour master is present and can lift a barrier. All the usual facilities are on site, with a good chandlery and a shop that sold basic provisions. The Harbour Lights Restaurant is also on site but this does close early in the evening.
Walton Backwaters is the setting for the Swallows and Amazons book Secret Water. https://en.wikipedia.org/wiki/Secret_Water
At high tide the area is a fantastic sailing venue, with plenty of creeks to explore. Departure and arrival is through a dredged and well buoyed channel. However, this is exposed to NE winds and even the East Coast Pilot book does not recommend entry in a strong NE when a sea has built up. Arrival on a rising tide is certainly a good idea.
Mistley is the furthest up the River Stour that most boats can sail. However, at high tide and using a shallow draft boat it is possible to reach Manningtree.
Anchored in the River Stour, off Erwarton Ness. This could be quite an exposed place. I anchored on the Low Water line and just touched the bottom but didn't actually dry out. However, as the tide turned the water was a little disturbed, causing the boat to move around. Heading further upstream to Holbrook may be a better location.
Sailing under the Orwell road bridge on the outskirts of Ipswich.
The River Stour and Orwell meet at Felixstowe, which is one of the largest ports in Europe. Basic advice is keep out of the way - there are recommended routes for yachts marked on the chart.
Heading along the coast towards the River Deben
At high tide it is possible to reach Beaumont Quay, which was built using stone from the old London bridge and was an active port until the 1930's.
Halfpenny Pier provides easy access to Harwich, its free for a short stay during the day.