Great - So you aren't starting from ground zero. Ok boost the amount of pectic ezyme up to double or triple the label recommendation (Normally 1/2 tsp/gallon. That craft store might just have what you need if the supply home beer makers. Wine makers and beer makers share a number of items that we all use. On the bentonite there isn't a big rush for that so I'd wait and see what happens in the first month or so after the fermentation finishes. SInce you say you're in rural area - yeah ordering might work out better for you but check out that craft brew store.
Sounds like are are pretty well prepared.
As to the pH testing - with plum wine especially if that juice is darker in color (Not golden colored) pH test strips are really hard to read.
If the juice is a golden color you might be able to use pH test strips but they can be tricky to read.
So if you are thinking about doing more wine making (Spring fruit harvests will be here before you know it. ) Then a pH meter can be had for under $50.00 I've seen them as low as $15 and of course the go all the way to astronomical. I can't recommend any in particular but if I was looking now I would look at two things beyond price. (Assuming looking at Amazon cause I'm a cheap charlie)
How many review? (Like to see over 100 reviews)
What percentage of reviews are 1 star and 2 star. If much more 10% are 1 star or a lot of 1 and 2 star - I'd be a little skeptical but I also have found some of the bad reviews were not even for the product where it was posted.
I've got 3 - My first lasted 4 years and now won't switch on. (Not sure how I got the 3rd one, think it was a customer good will gift for another product that failed.) The second one is probably going to be pretty good: It's the old version of this one.
https://www.amazon.com/Dr-meter-Upg...s=ph+Meter+wine+making&qid=1611452486&sr=8-24
Keep us posted.