@coldreactive That video only covers the very basic idea and process of affixing and don't go much about details.
@Zagi So making practice on you own is a good way to know about the details of affixing, still I'd like to make some suggestions for affixing practices.
Not to use "Augmentation Aid +30%" for practices. This item worth 20 EX-Cubes and too precious for practice uses.
Always have eyes on "Your Cash" shown on the top right corner. Affixing can take Meseta away in enormous speed, so retreating when you are losing too much is important.
Don't touch your main equipment. Probably, this is a very arguable point. But affixing is a very complicated process. And it's also a process very hard to recover from failures or mistakes. So I'd rather recommend to be 100% sure about what you are going to do and what are the risks involved, before tackling your main equipment.
Going back to the question on the OP, you can "grow" affixes like Might I - II - III, but probably, buying material weapons already having Might III will be cheaper.
And just one more thing I want to comment is that affixing is not a process we can add them one by one. Let's suppose I want to add Quartz Soul and Might III on my base weapon.
(I'm writing this example just seeing wiki without checking the actual %s, so forgive me if there are some mistakes)
Quartz Soul + Quartz Soul + Quartz Soul = 80%. Let's use Augmentation Aid +30% to make this 100% (suppose this is not a practice).
- xxx xxx (base weapon) + Quartz Soul xxx + Quartz Soul xxx + Quartz Soul xxx + Augmentation Aid +30%
This will give me Quartz Soul xxx on my base weapon. Then add Might III next?
Might III + Might III = 80%, but Quartz Soul gives +20% bonus to Might III, so I can go with 2 Might IIIs.
- Quartz Soul xxx (base weapon) + Might III xxx + Might III xxx
Will this work? No. In this case, Might III will be a 100% success, but having only one Quartz Soul won't allow Quartz to be inherited to the result. I must add 2 more Quartz Soul to give it a realistic chance of 80%.
- Quartz Soul xxx (base weapon) + Might III xxx + Might III xxx + Quartz Soul xxx + Quartz Soul xxx
This gives a 100% chance for Might III and 80% change for Quartz Soul. If I add Aid + 30%, then I can omit one Might III thanks to the 30% modifier.
- Quartz Soul xxx (base weapon) + Might III xxx + Quartz Soul xxx + Quartz Soul xxx + Augmentation Aid +30%
This will give me 100% success on both. Maybe you noticed that the first step of adding Quartz Soul was almost a waste.
This example only handles 2 affixes for simplicity, but if I was going for a 3 slot weapon, adding a 3rd affix to Quartz Soul Might III xxx is a daunting task since I need to care about keeping the Quartz Soul and Might III as well as adding a new affix. I hope I could illustrated the difficulties we meet when we are going to add affixes one by one.
So in practical affixing, we need to define our final goal first. How many slots do we want and what affixes do we choose. Then, from the goal, we have to calculate back the material needed.
It's quite a complicated process, so in many cases, it's easier to follow some recipes deviced by affix masters. I'm also a noob about affixing, so waiting some solid recipes for NA
(Note: in the example above, I want to make it a failure, so added affixes in the order of Quartz then Might III, but if I did it in Might III - Quartz order, the one by one way worked. But even so, it won't work with 3 or more slots cases)
EDIT: a while after writing this post, I noticed that in the current NA environment, if we want some serious attempt to add Might type affix, then using the Might IV augment factor of melee type Sigma series weapons is a common answer. So using Might IV instead of Might III can also be a choice.