1) I would like to know how much is enough in regards to success set.
1) just get as much as you reasonably can. Using (pure water) Alchemy as an example;
each 25 INT = +1% success rate
each +5% Melee to Dark = +1% success rate
Production Ticket
Fortune colour
Alchemy success rate +1% relics?
Melee to Dark could come from:
a) Equips (obviously, use Stavros)
b) AI (expensive, only recomended if you have extra unused AI pages)
c) xtals (10% xtals are ~100m, 15% on Additional xtals are ~150-200m each)
d) consumables (light drink)
e) skills (i don't know any, apart from pet skill All Around, Enchanter's Origin(???), or standing in another Alchemist's Prod Workshop)
You can claim Production Tickets on multiple characters on the same device, put the tickets in storage, then withdraw them on the character you want.
No. It will make you succeed more often (less fails, which will mean less potential to lose mats).
In my experience, the difficulty is a %. Above a certain number (maybe 90%), the difficulty is displayed as [Very Easy]. But you can still make the recipe easier by getting more success rate buffs. I was able to refine 14 EDG s to q15 with only 1 fail, by maxing out almost every source of success rate (it never changed from [Very Easy]).
If you're not failing that much, then use it. Here's an example with FPF I made.
When I made a stack of FPF with Cooking Charm, I failed 4 times and made x235 (and then crafted the 4 that I failed again, and made x10).
When I made a stack of FPF with Secret Prod Book, I failed 8 times & destroyed 7-8 of each mat, but made x260.
I can use SPB most of the time, because I'm usually overleveling the recipe a lot, which provides a huge benefit, but if the recipe is close to your level, or if your success set isn't very great, SPB is not for you (yet).
For now, just buy melee to neutral gear, like Eventail III. That will greatly boost your great successing, and even though you will fail more due to not using success set, you'll barely lose mats, so you can just prod the leftover mats again. If you're not an Alchemist, then Eve III is is almost as good as SPB (+10% great success rate, compared to +11% of SPB)