For Black market, this is the list of item you will need to take account of:
Blake dagger (item to make lightling madness)
Lighting madness (coz it require both ancient relic and Blake dagger, if buy this is also ok)
Naomi Wraith (need a lot coz all INT need this to create Moon Deck and Kiss of Death)
Witch hat
Marina Will
Ancient Relic
Ulti relic (coz its cheap and u need a lot of it.)
Brutus demise (coz the amount u need is 2-3x compare to dragon mind)
Dragon Mind

Reset too much will consume a lot of gems as well (i rarely reset SS as well). Keep it minimum and this way u don't need to spam that much gem to reset stamina.
try dont reset and see how much stamina u consume.
1* based hero (those that require only 10 SS to summon) don't need to reset as their SS can be gain through pulling 90k box.

Keep Gabriel, Naomi SS for farm at later stage. (they are not necessary yet) Wait till CH 13 and 14 open only farm them and u will gain item fragment for orange item as well.

Avoid farming CH 1-3 coz those stage SS drop rate is very low (you are wasting stamina)
Farm higher stage consume more stamina but their SS drop rate is so much higher

those chapter low drop rate so low, like every 108 stamina u will waste 1 ss, 36 stamina. item is shit as well. People farm higher stage ss along with items (win-win situation). No matter what, item > SS. If lets say your so fast max the SS, later on you don't have the reason to farm the stage any more and thus, you will get lesser specify item that u need. E.g. Devil edge : farmable at Sarpa Stage 8. This item you will at least need 100 of them through out the game (means 2000 fragments and how do u get to collect that much if you don't have a reason to farm his stage any more?). Relying only 1 source is not enough, you'll end up bottle necking your progression.  If you focus on 1 stage a day, by the time you get to 5* the hero you already gain a few hundreds of the specific fragments.

Probably its hard for you to understand why people slow down their SS farm but there must be a reason people tell u to slow down. Get to know the concept of this game is long term. No point rushing. At Purple 3 and above, gaining higher rank gave boost 100+ stats or so. But 1 or 2 item of the stage already give better stats.
Specific hero with important items at near end of chapter 10-14
Gabriel : Dragon mind
Tiny : witch hat and ulti relic
Raven : naomi wraith
Naomi: witch hat
Sirius : ulti relic and brutus demise
Lilith : Armor of Boras
Buster : Dragon mind and Brutus demise
Well, you can ignore what i said above coz there is a better way which is u will gonna spend and spend more money into this game. Be a super VIP spender and you will win this game 

Evil dragon scale and lilith bathrobe is worth to get.

Bathrobe.
Jackhammer need for healer hero only (not so important yet). Later you will get some.