i have run my Orbes with SME ,Rega derivitives ,Hadcocks,morch and Graham arms at .present i am using a Mission 774 none of the arms i have tried have been a problem as Michell will make a custom amboard to suit your choice. John Michell developed the Orbe with the SME arm as his standard so its fair to say that a match is there.As with all hi fi i would always say you get what you pay for so go for the best you can afford at the time as the and up grade when you can.
cartridges ,as already stated are a matter of taste but again "yer pays yer pennies"
out of interest i am making a 12 inch arm tube for the Mission that should give the guys at Michell some head aches.
cheers and hi ray