My suggestion would be to first do the platter. After the platter is complete, then the rim drive since you won't have to fiddle around with the rim drive set-up more than once (it's not really much of a pain, but still...). Then do the new arm.
IMO, the platter will make the most difference.
There are some mounting options to consider with the rim drive. Review all the information you can get your hands on. You may want to consider mounting the rim drive on a "slider" so that it's easier to engage / disengage with the correct pressure against the platter. (Hint: look at the construction of drawers and sliding kitchen shelves.)
If the new platter comes with an entire bearing ass'y, let me know. I might be able to help you get rid of that old platter / bearing assembly.
IMO, the platter will make the most difference.
There are some mounting options to consider with the rim drive. Review all the information you can get your hands on. You may want to consider mounting the rim drive on a "slider" so that it's easier to engage / disengage with the correct pressure against the platter. (Hint: look at the construction of drawers and sliding kitchen shelves.)
If the new platter comes with an entire bearing ass'y, let me know. I might be able to help you get rid of that old platter / bearing assembly.