Ah, the forever asked question; Merchanting.

I hate having to rely on Gachapon and NX to get my money.
It's rarely been a problem till now.
I have 60 mill pure mesos. After selling my 86 attack Deadly fin, 71 attack wagner and 6 dex black snowshoes, I'll have about 90 mill HOPEFULLY.

The goal I want to reach is 250mil.

The problem: I've never merchanted in my life. D:

What is the best item to merchant (Khaini)?
I know it's a very open question, just put your personal favorite.
also how long would this operation take?
I can get a shop, so that's not a problem.

Thanks so much,
zach