I'm a beginner windsurfer looking for a board and kit I can progress on. I'm 55kg female, 5ft4 if that helps, and have been looking at starboard and jp brands though open to suggestion, any advice would be super helpful

NuBee,
but one of the many threads that pertain to starting.
www.seabreeze.com.au/forums/Windsurfing/General/Beginner-board

Search engine on top helps find these.
Your inquiry , contains some details, but post picture

you want something , that's large enough to offer a platform, center board desirable. If you chose a dedicated beginner board, you can keep this to use on light wind days, but you will outgrow it, and need something smaller.
A sail that's small enough to handle.
very few are as light as you.

as usual height and weight are a good start
however, there are MANY more factors

i call them W5 = who, where , what, when and not the why

who = have you done water sports before , good swimmer, strong vs not so strong , etc
where = obvious
what = do you hope to do
when = do you have time to do, can you travel
why = obvious

and W6 = welcome to the best water sport in the world