First relic opens like it says it would: After you manage to get final tier item in level 1. However, even with all 8 levels are maxed out now, I cannot seem to unlock any other ones. Are they not implemented yet or the problem is with my game?

When you become able to merge two level 2s into a level 3 you find that you only get 3 points for the level 3, which is the same as if you sold three level 1s but it takes four level 2s to make a level 3. That means you are losing 1 point, and I bet that the same continues if you go up to level 4 and so on. There is no point to merging then since its more effective to just sell the level 1s......

what does auto sell do? and how do you use it?

According to help page relics are supposed to be unlocked when you upgrade some item to level 12 but first relic was unlocked already when I checked it while having just level 2 items. Bought 3 upgrades total and still was able to do a reset for 2x multiplier. Is doesn't seem like an intended behavior....

I've gotten relics 1, 2, 3, 4, 5 and 8 but now I'm unable to progress. Getting 6 and 7 isn't working.