Hello and welcome to permies!
Full self sufficiency is a tad difficult on a couple of acres even on good land - it all depends though. Marshland can be very productive for biomass and other stuff too, but access can be difficult, and seasonal flooding can make things even more awkward.
Willow has loads of uses - biomass fuel and weaving material are two that spring to mind. Other
trees that don't mind it a bit damp in my
experience are alder and aspen, although the latter has a habit of dying back and then coming back where it feels like! Food plants are possible, even in the UK, but it all depends...
Questions:
What are your summers like? Is the land wet all year, or just boggy in winter or after rainfall? Do you have acidic soil? windy or sea exposure?
You may find my
chinampa thread of interest as providing some starting points. I've not updated it recently - the area is still establishing, although I could try harvesting a few wapato this winter perhaps.
From personal experience I can recommend skirret and marsh woundwort as good for eating that like it damp and relatively cool. I'd dearly love to try bulrush (reedmace/cattails) Typha latifolia, but you need space for that to spread (which it sounds like you have...) Another thing that would be really cool is a crannog style house, but you'd have to think hard about sewage cycling.
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