well , 1 good strategy is to reroll the account at the begining a couple times till you roll a black or good plat from your first 2-3 rolls ( getting 10-15 sc at the begining is rather easy. You just have to 3 star the first missions )
If you dont get a good unit , just make another account.
As a rule of thumb , any plat princess , mage , soldier are pretty good units. Getting a black at start is even better. For example , my first account is a non black (other then the event/trading post units) account. I have completed every event till now without an issue.
My second account got a first roll nanaly (i didn't rerolled for it. i got straight up lucky) , and then i decided to trow a couple bucks in it , and got 2 more blacks.
Blacks can and will make your gameplay easier , but the truth is that 99% of this game can be completed with silver/event units.
In the end its up to you , but if you feel that you were unlucky , you can do as i did and try to make a new account. I ended up playing on both. First one for the challenge , and the second one for fun. I also get to experience different units and use different strategies and that can give you some insight into what is good and what is not...
So.. the month is ending and I'm gonna be getting a S Legend. What I want to know is what are the chances of getting a black from the ticket?
15% chance
Is there any way to farm silver+ units or do you just need to get lucky at the shrine?
Event maps, trading post units (via demon crystals) and base summon are your only farmable options. If you're not particularly interested in a given event unit it can be worthwhile to farm maps anyway for silvers.