>>>Have lunch along the Southend seafront at one of the cafes opposite the beach
In my opinion, that advice possibly needs to be treated with caution (or, at least, with a bit of geographical knowledge thrown in).
There are plenty of cafés opposite the beach at the 'brash' end of Southend seafront (which you'll get to if you head down the main High Street and turn left when you arrive at the seafront), surrounded by amusement arcades and some rather rough pubs. Some of them are actually OK but they do tend to be of the 'working man's caff' and 'chips with everything' type.
However if you turn right upon your arrival at the seafront you'll find some much nicer places, which are also opposite the beach. The first place you'll come to is Fisherman' Wharf
http://www.fishermanswharfsouthend.co.uk/
which is generally very well-reviewed (but with some clearly dissenting voices):
http://www.tripadvisor.co.uk/Restaurant_Review-g503790-d1812154-Reviews-Fishermans_Wharf-Southend_on_Sea_Essex_England.html
However I recommend walking for a few minutes longer until you reach Palmeira Arches, where you'll 13 eateries side by side:
http://www.southendstandard.co.uk/news/8995556.100_years_of_food_under_the_arches/
including, for example, the Fountain Café
http://www.tripadvisor.co.uk/ShowUserReviews-g503795-d4332578-r167784326-The_Fountain_Cafe-Westcliff_on_Sea_Southend_on_Sea_Essex_England.html
In my opinion, those cafés are far better than those at the other end of the seafront.