Where to begin with old deck?

Hi there,
We just bought an apartment with a rooftop deck that we'd like to prep for the winter. I understood from your website that first and foremost we'd have to use the cleaning kit and then stain or seal it.
The deck looks like it was never really treated and preserved properly, it looks already gray and dull. Also, I have no idea what type of wood it is made of.
Does it seem like a good idea to use the Restore-a-Deck Cleaning Kit and a TWP stain or sealer or would you have any further advice?
We might sell the apartment again in a few years time and don't want to put too much effort into it as the next buyer might want to build a new one.
I would very much appreciate to hear your thoughts on how to tackle this properly as we're new home owners and have no clue what we're doing! 😉
Thanks in advance,
Alex