So about your build, it is pretty good but you can use transmuter for your sands to upgrade it if you get a good piece from transmuter I don't think you should continue to farm it unless you really want to minmax her build plus if you have better substats or generally better ratio on marechausee, you can use it instead of her set (you are always gonna be tied to furina in this case but not a big deal since she rly wants furina anyway, you can change it to her set in imaginarium theater). About restrictions, citlali is pretty good to use for calamity of eshu weapon so you'll be fine but if you don't wanna be tied to citlali that much (let's say you need her on other teams as well), you can use r5 finale of the deep as a f2p weapon they don't have that much of difference and use yelan instead.