I wore a bike jersey for the last 2 years and it worked great as I could store all my nutrition and an empty water bottle in back (wore small camel bak my first year). My only issue was of fit. The arms are a little tight so it started bugging me after a while. This year I am going with a biking vest I can wear over a tech t-shirt:
Visor and no sunglasses for me. Will carry some light gloves as my hands tend to get cold at altitude. Definitely would wear gloves if doing the Marathon but am an Ascenter so only need them for temp and not diggers. Weather looks decent so no jacket for me.
Good Luck to all!