A better approach is to do a ring-around. A ring-around, classically, is a 3x3 chart of nine photographs, all of the same scene, arranged in three rows of three. Start with a scene of normal contrast. Horizontally, the rows are “underexposed, “normally exposed,” and “overexposed,” and the vertical columns are “under-developed,” “normally developed,” and “overdeveloped.” This gives visual confirmation of nine different combinations of exposure and development.
A third or half a stop is a waste, it's not enough difference for starting out. Use full stops, and -15%, manufacturer's time, and +10% as under, regular and overdeveloped. Use the same, normal agitation. You need to see the differences.
I learned to print them with the same contrast and enlarger exposure time, but this was a bit controversial; some advocated that each negative should be printed the best it could be. I always opted for the former because it accentuates rather than hides the differences in exposure and development. Proponents of the other approach usually argued that whatever your neg looks like you are going to do your best to print it well. It probably doesn't matter, except the latter approach also gives you more of an idea of how hard or easy a negative will be to print. For scans, to understand your negatives, I'd suggest basic adjustments given that your raw scans should be pretty flat, uninteresting and a long way from your optimised images.
This is the best way to start to calibrate your negs. From there you can fine tune exposure, development time and agitation. With agitation, I found that decreasing it gave my negs streaks and was not different from just decreasing time. I did a long experiment to assess if there was any difference between decreasing time and decreasing agitation and for my purposes the difference was so minimal that the risk of streaks wasn't worth it. So I use developers with long normal development times and adjust purely by time, not by changing agitation.
A roll of E6 film and some scenes with regular contrast will tell you if your meter is behaving.
You need to figure out what works for you.
Marty