Mm, it's important to understand the benefits of synthing.
1) Transfer skills to other pieces of equipment. This is pretty powerful in its own right. Each piece of equipment has its own condition deterioration rate, which reduces on attacking, receiving damage, or both. A lot of equipment with great skills loses condition on attacking (which is generally unfavorable, you should be doing more attacking than receiving damage). So you can synth those abilities over to a more favorable piece of gear that doesn't deteriorate as easily. Similarly, you can shift abilities to gear that provides the stats you want to emphasize.
2) Raise the condition of equipment. Condition multiplies the effect of equipment boosters, as well as the stats on the item itself.
If you have a Nietono no shana, a dengeki sword with 50% SAT (and 50% fire, but that's not important here), and increase its condition to 140%, it will now have a SAT bonus of 70%.
Now, back to the original Nietono no shana. Say we had a Plug-S R Arm booster, giving us +45% to R-Arm equipment. With the original, unupgraded sword in the right hand, you get a 95% SAT bonus (50 original plus 45 from the equipment booster). However, if you raise its condition to 140%, you'll now get a 133% SAT bonus (70 upgraded sword plus 45*1.4=63 from the equipment booster)
To give you an idea of how ridiculous it gets later on, the maximum condition for an item is 694% and the maximum for a single booster is +255%. So if you use a 694% condition hat with a maxed Plug-L Head booster, every stat that the hat has a bonus in will be increased by at least +1770% (18.7 times original stat), since it's not including the actual bonuses on the item itself.
As for the actual shit you asked about:
Rank 1-2 equipment: 8 points
Rank 3-4 equipment: 9 points
Rank 5-6 equipment: 10 points
Dengeki equipment: 10 points
Unlosing Equipment (cape must be 2star and above): 10 points
1star Unlosing Cape (failure cape): 3 points
The blacksmith skill only affects how many times you can call them per dungeon, I think. Might also affect repair prices, I don't know.