How often to you clean vinyl and the needle?

Record with brush before every play.

Stylus as needed = rarely.

I clean an LP on my Degritter when it first acquire it. If it's brand new I just do a DW cycle. If I bought it used I do a two-cycle clean, once with detergent followed by a DW rinse. After that, I clean the record as needed.

With my cartridges, I clean the stylus tip with the Lyra SPT and provided soft brush before each listening session. Then I use one of those round carbon stylus brushes after each side or at least each record (two sides). After about every 50 hours of use I clean my stylus with the Flux HiFi ultrasonic cleaner, but for no longer than 10-15 secs.

Records once if I play them rarely, maybe every year if I play them often. Needle-before playing each side. I hate vinyl and love tape.

Every record new or used goes thru my RCM, VPI HW17, before first play,  Then every record is treated with LAST.  Then every record gets a quick brush before each play on each side every time.  If any record gets noisy it goes thru the RCM again.  Stylus is lightly brushed with Stylast before each side is played.  I inspect the stylus regularly with a lighted magnifying glass several times per week.  If there is any sign of buildup (rare) I clean the stylus with an ultrasonic cleaner that I bought on Amazon that is made by Hudson.  It is remarkably effective.  Every six months the stylus is inspected using my Wild-Herrbrugg microscope.  This is mostly to monitor for wear.

I treat records with Last too, once. They even sound a touch better than without it.