Stowmarket is a Gate Box and is a Grade 2, there is also Saxmundham Grade 6, Bury is time limited with resignalling underwayColchester has a PSB at the North Station, where the main link is Grade 8. They cover the main line from Chitts Hill, just South of Colchester to Norwich, the Clacton/Walton on the Naze Branch, and the Felixstowe Branch.
The NYL workstations, which cover Brundall/Lowestoft/Great Yarmouth are also located there, and they are a Grade 4.
Other than that there is Parkeston Signal Box, which is a Grade 4 and Stowmarket Gate Box, which I am unsure of the Grade.
Bury Yard is a little bit further along heading towards Cambridge but that is due to be abolished very soon as part of the Cambridge resignalling project.
Other than these boxes there are no others in the area. Shift patterns are majority 12 hours, but there a few exceptions which still work an 8 hour roster. Hope this helps.
As you say Colchester ASC is Grade 8 Main Link, and the NYL (Norwich, Yarmouth, Lowestoft) Grade 4 Axle Counter.
NYL is a good route into the Main link at Colchester.