There's only 3 paved roads going up to CH IIRC, none of them highways if that's what you call as fast road with at least two lanes in each direction. These roads are single lane for the most part with some double passing lanes on one of the highways The old road is the one some maps label at 59 and the closest of the main north-south highway to .KL. There's another, 185 that goes to/from the same highway near Ipoh. Not as scenic and (much) more traffic. Haven't gone the other way on 185 towards the east coast. These latter two routes (or 185) are none of your concern for a day trip.
BOH plantation needs no appointment. Just go there (not sure if there is a processing plant tour), walk around the plantation, and sample their offerings (nothing complimentary IIRC but the visit was free 3 1/2 years ago). There's another plantation just before you get to Tanah Rata but it is a scenic and refreshment stop more than anything else (do try teh tarik but only at a mamak (muslim Indian) diner. The "teh tarik" that BOH and the other place offers are made from 3-in-1 powder mix (that they're all too happy to sell you).
I can't say there is much to see in Tanah Rata or beyond, other than what must be one of the largest fleets of Land Rovers (nothing emotely new, all are probably 40-50+ years old). It'll be like going to Havana for a vintage Land Rover enthusiast. Otherwise just a lot of development (high rise hotels), intense agriculture, tourist traps, and no increase in road capacity hence bad, bad traffic congestion.
Main attraction of the place? It's cool. The British used it to get away from the heat (same goes, to a lesser extent, for Fraser Hill and Penang Hill among others).