1. Microupgrade must be all completed before you unlock next mk, check wiki for each mk unlock rank for the turret.
example A, if you play not often, you can just go back to tanki to use each sale to microupgrade 1 step, and dont play much before next sale, make sure you also save enough crystal by play minimum with those free gifts to use for next sale,
example B, if you play a lot, make sure you microupgrade without speedup as soon as possible, so you have more crystal to micrupgrade without sale, so you dont rely on sale to upgrade, but use microupgrade as much as possible. That way, you always at max GS than others, and get next mk at 0 crystal when max current 10/10mu, worst is you at 9/10 after accidental rankup, then you pay double price in total. Since next mk is full price, they used to be 90% off, but tanki kill off tgat update
Example C, you only microupgrade to 5/10, use sale to buy next mk, you are half half. Dont mu more than 5step if you ranking to unlock next mod before next 50% sale
 
2. In mobile, yes.
In desktop, yes
3. You get too much 40k crystal if you rank up every 3 day for non stop player, so they give 1 container that mostly give 1k crystal to laugh at your effort for playing too much tanki

I got rico XT from 3 month ago in the challenge,
Xt skin can be the final reward in battle pass

if 1 year no login, they will be removed from friend system to save space, or to force people play

supplies need to be used from supply, or pickup
booster drone, defender drone, sabotuer drone, hyperion which used more than 1 supply, are count as 1 usage (previously it counts 3 but the some updates make it count as 1 only)
only Camper drone, Mechanic drone, criss drone, miner drone can help you reduce cooldown speed and use supplies faster