1. Its nothing much important, actually. To alchemize, just bring 2 weapons of the same exact name (for example, Broad Wings and Broad Wings, NOT Broad Wings and Broad Zhen), and he'll mix them to you, adding a +1 to the name. The alchemizing's effect is to give a small attack boost to the weapon (ATK multiplied in .25, .50, .75, 1, 1.25).
So, lets say you wanna have a Spin Piney at max. customization (+5), and you somehow have all the Spin Pineys needed already. So, you talk to him, select the weapons, and it goes like this
Spin Piney + Spin Piney = Spin Piney+1 (x.25)
Spin Piney+1 + Spin Piney = Spin Piney+2 (x .50)
Spin Piney+2 + Spin Piney = Spin Piney+3 (x .75)
Spin Piney+3 + Spin Piney = Spin Piney+4 (x 1)
Spin Piney+4 + Spin Piney = Spin Piney+5 (x 1.25)
That is all...
And, once you have a weapon at +5, you can use it to alchemize any other weapon of the same kind (in this case, Dual Swords), but only counts as 1.
So, you can use it for a Spin Needle like this
Spin Piney+5 + Spin Needle = Spin Needle +1

2. Armor of lvl below 30 only has 1 slot to put items. Armor of lvl 31-50 has 2 (i believe that's right)
Indeed, it shows you 3 slots, but only either 1 or 2 are avaliable at the moment on each armor. And at least in Vol. 1, there's no way to increase the number of slots each armor has

With the Spin Piney+5 and Spin Needle thing...it goes like this
Spin Piney is at it's max alchem. (+5)
If the weapon is within 10 levels of each the other one, it can be alchemizized.

NOTE: When I said "10 levels", I mean 10 levels UP. You cannot alchem. down.

So lets say (for instence) I have a Broad Legged+5, and I also have a Broad Maiden. In the alchem. menu, I'd select Broad Maiden, then as a suppliment weapon (the weapon you're adding on) I'd choose Broad Legged+5. When it's finished, I should have a Broad Maiden+1, since for every time you alchem. a weapon, it's alchemy rate goes up one (+1).

NOTE: (This, yes, has happened to me) If you're trying to alchem. a weapon that you bought at a store, make sure that the number of that weapon in your inventory is six (6). Seriously, if you bring five, thinking the outcome will be +5, it will be +4. This is why:
You have in your inventory a total of 5 Spin Kougas, that you will now alchem. together.
Spin Kouga (#1) + Spin Kouga (#2) = Spin Kouga+1
Spin Kouga+1 (#1) + Spin Kouga (#3) = Spin Kouga+2
Spin Kouga+2 (#1) + Spin Kouga (#4) = Spin Kouga+3
Spin Kouga+3 (#1) + Spin Kouga (#5) = Spin Kouga+4

In simple terms, your first Spin Kouga (#1) is a base. Now your just adding the other onto that. So here's a quick helper
The number of that weapon you have - 1 = Your +whatever

Example: 3 Magic Hoseis - 1 = Magic Hosei+2


And yeah, the slot availability is for weapons, armor, and accessories.

I missed that part or I read quickly over it. That would solve it.



Thanks.