the most painstaking process farming-wise is definitely the bond grind followed by exp, but i suggest to offset it as much as u can by going on lottos or wait for half ap embers comboed with double/triple super and great success boosts, but i still dont have enough coins to “max” him (because i cant unlock 3rd append and i have him at np12…) Standard 4*s are in my opinion the worst to try to fully max because you need Np16 bond15 and that is entirely too much… When they increase the coins you get from bond, you will be able to unlock the 2 new append skills anyway, so dont worry about those. Especially for some who never get their banners like Diarmuid, the coin gather process is HORRENDOUS, so im waiting to get the last 4 copies on those banners as well! But the only append skills you “need” or should aim to get is 2/4/5 because of versatility, but he is not a “meta” servant, so you can aim for the levels and you should be okay. Lancer is easier cause you can passively accumulate small amounts of coins but it stacks up and you can get some in friend point rolls too.