Welcome to the addiction.
You made a good choice with the LCT.
You will need something to measure the OAL (calipers) and when you get to loading rifle, a bullet comparator so you can measure the OAL accurately.
A lot of people use Trail Boss and love it. It is a really good powder for beginners as it will be impossible to double charge. The downside is it is a powder puff load.
My preferred powder for light target loads in .357 is W231. The downside is it will be pretty small down in that case, so you will have to pay attention when loading. The auto indexing of the LCT will help in avoiding double charges, but denser powders are always a risk in those long deep cases.
Have fun, good luck.
When asked what qualities he most valued in his generals, Napoleon said, "give me lucky ones."