Wonderful idea, Maureen - planning some fantasy travel, which may or may not be possible in a post-Covid world.
So, what would you need to know about Essex and where the best walking is to be found? First, Essex is very large county - in UK terms, that is - and more diverse than some English regions. South Essex is really outer London. North Essex runs up to the Suffolk border and is much more rural, with historic villages, such as the one I live in, and ancient woodlands. There is an extensive coastline, but you are mostly talking marshland and mud. There are tidal estuaries where mud is a big feature too.
From a centre such as Colchester you would be well-placed to explore both the coastal areas and the North Essex/ South Suffolk border. Colchester has a castle with a Roman museum - an unparalleled collection of Roman artefacts. You could drive north to Dedham and walk along the river to Flatford Mill, much painted by John Constable. Or you could watch the tide tables and go across the causeway to Mersea island to see birds in season.
A number of long and short footpaths are on offer. In fact, we almost always just drive a couple of miles north, park up and walk in the woodlands on public rights of way. This is really important at this time of year as Essex is very flat in general and the field paths can be impassable with wet mud.
http://www.gps-routes.co.uk/routes/home.nsf/county-walks/Essex This is a site which lists a range from the 85 mile Essex Way to much shorter strolls. Room for much fantasy planning here.
A short drive will take you to the famous villages of Lavenham and Long Melford - historic wool towns with spectacular churches and many ancient buildings. Sudbury, a small market town, still has four working silk mills and is well worth a visit. These are in Suffolk, of course, but are very similar in character to Coggeshall, the Essex village where I live. Here the must-see is Paycocke's House, home of Thomas Paycocke, the wool merchant who built it in 1508. The carvings inside and out are spectacular.
Mind you, I'm not sure that I would announce to friends that I was holidaying in Essex. The county has acquired a reputation for being brash and vulgar - there's a reality tv show called "The Only Way is Essex". I've never seen it, but, like others of its kind, it features girls heavy on false eyelashes and boys who have spent too long in the gym. North Essex is more rural: Wellington boots are a good choice of footwear here.