A great source of information for all Tri-5 Pontiacs is Larry Gordon's Safari site:
https://www.pontiacsafari.com/
Don't be fooled about the depth and breadth of the Safari info; you will find mechanical info there (and more) relevant across the line.
As for oil, I use Lucas Hot Rod & Classic 10-40 in my '63. Synthetic is fine, and I use Mobil 1 in my more modern cars, but tolerances being what they are, and the need for zinc in these older engines being what it is, I prefer an organic oil with high zinc content. (Back in the day - 40 years ago - I ran Valvoline 20-50 exclusively; I've found no need for that since the engine rebuild, and the 10-40 is definitely easier starting in cold weather.)
Now, about that wiper motor...
The electric motor was on option on my '56. Checking on '55....
It does not look like the electric wipers were offered for '55:
https://www.pontiacsafari.com/55/Acc...esPamphlet.pdf
Vacuum wipers should work well, but will slow down going uphill or under other periods of low engine vacuum (sounds funny, but that's a fact of life).
There are some very knowledgeable people here (including Larry). Another piece of advice I'd give you is to collect as much sales and parts literature as you can, whether original or reprint (or perhaps better, in digital format). Another book I have which is quite handy is an interchange guide for Chevy, Pontiac, Olds, and Buick. Often the same NOS part with a non-Chevy part number can be much more expensive (or unobtainium) than a standard Chevy part which fits, connects, and works just the same.
Anyway, welcome to the group. Please *do* ask questions and provide as much detail as possible (pics are always a plus).