1. What type of card do use?
I setup my own card type with the information I found most valuable in the past.
Sentence, Sentence with furigana, Translation, Word, Meaning
Translation, Meaning are in English
When reviewing I have the card display the sentence without furigana initially, the rest of the fields are to check myself after I read the sentence.
2. How many words you can learn in one our counting reviews?
I found 8 was the sweet spot for me but I also change it based on how many reviews Iām getting daily and motivation. I donāt want to spend a lot of time on anki reviews every day to avoid burning out so if the review count is increasing, I might stop learning new words for a week or so.
3. How much seconds/card you go while doing reviews?
My average answer time is 17.89 seconds but sometimes I do reviews while doing other things and just leave it open and answer as I go so itās not really a very reliable metric in my case.
4. How much seconds/card you spend on cards you learning?
I canāt find this metric at the moment but Iād imagine itās about the same. I usually just mix the learning cards in with the reviews so they are randomly dispersed. But I also make all my own anki cards, so my learning cards are always something Iāve seen before (because I made the card)
5. Have you tried using Anki when you knew only 50-200 words? Was it bad? Have your ability to learn new words increased drastically since then?
I did not try anki back then but I would have if I knew about it. I like it alot and have used anki for learning other things in my life as well. I definitely feel the difference when I use anki compared to when I donāt as far as my ability to learn.
On a side note: I did use anki to learn kanji using RTK (remember the kanji) method. I spent about 300 days doing 15 kanji a day every day. I was doing about 150-200 reviews a day. I never missed a day. I started out knowing maybe 300ish kanji. I got through the entire deck of 3007 kanji cards and wrote stories for each one to remember them. That was like 2 years ago and I stopped reviewing the deck after about 6 months of reviews with no new cards. Iām not a kanji expert. But I still think it was really helpful. Whenever I see new words now, it is rare to see a kanji I havenāt seen before. Even if I donāt remember the meaning or the reading, Iām not as overwhelmed. It has made learning new words much easier.
6. Maybe you use some kind of memory palaces to remember wordsā readings (for when you know the meaning and need to extract how word sounds from head)? Or maybe you use other techniques?
I donāt use any techniques. I made stories from the radicals to help with my kanji study while doing RTK, but with new words I just brute force it. It was hard to accept that some words just donāt stick and I felt really bad when a card would get marked as a leech and suspended but if you are adding cards regularly, the one word is insignificant amongst the many others youāll be studying. You can always make a new card for the leeches later and maybe then youāll be in a better position to memorize it. If you spend too much time worrying about leeches youāll waste time working on a single word when you couldāve learned 2-5 other words that stick easier.
Sorry I wrote so much, thanks for reading if you did. My only tip for anki is when I was doing 15 new kanji every day for 300 days, 150-200 reviews per day felt miserable at times. It made it worse when I would add a new card and kept getting it wrong repeatedly. However, I found a pattern emerged. When I would push through despite failing the same card repeatedly. Around day 3 I felt really bad. It felt hopeless. But around day 4 or 5, it would randomly click. Iād suddenly start getting it right every time. Consistency is really the only thing that matters. Even if youāre struggling and it feels hopeless. It gets easier. Then thatās when you make it hard again 
Explains the weird phrasing.