A quick way to gain stats at lower levels is taking advantage of the low time cooldown of stamina refill and getting stuck at some part of stages (in the past most users of this forum was insanely at stage 1 when i was boosting to 3 and the reason is one, stamina cost). This will allow you to get some pero to try gacha or any other stuff.

The low quantity of cards also helps to get one at level 100 and get the chance to level other (even higher rarity cards) when gacha find one of them (give additional pero in stage). At elite guard you can use that event to keep stamina cost low and roll for cards (3 stamina per roll).

However, at lower levels SED gain is slower via card level than card quantity. Priorize Moe type cards to level with wild cards (until lvl 60), then babe cards and don't rush beyond stage 2 until lvl 30 (7-9 stamina cost per roll), the same warning for Perogambit which use a lot of stamina to explore (below 200 is pretty hard).

About pero, Nutaku removed the discount using pero over gacha packs, the only strategy in a few words is stack pero (throw pies against the friends of your friends if you completed quests or are out of stamina) and store carefully some special stuff like Guaranteed SR gacha tickets and card reveals until when you really need it.

And consider starter/booster packs if you can cash in game (those are offered for a limited time at lower levels, but boosters offered at last days of EG or Perogambit are better).