I also live on the coast - look forward to hearing what is growing for you - this is my first year of growing veg in garden. Dining room table is covered with seed trays!! Would love a greenhouse but think garden too exposed to the elements and gales especially in winter.
Have thought about seaweed also but as Flummery has said I've read that using it via little in compost bin is best but as I haven't tried I don't know for sure.

Good luck