A few questions. Hope someone can help :)

[Buffs Mad]

1. How exactly youth academy works? I couldn't find much info on wiki. I mean, what determines their skills besides level of youth academy's level, what are chances to land a good player, what you usually do with players from them and can I just sign them when they appear, or I have to pay tokens for them?

The Academy level determines how long it takes to produce the players. The Q is generated. The Token cost of a player is closely determined by their Q, the higher the Q is towards 5* the higher the cost. The market value (MV) seems to be generated rather than fixed although they are usually high........ The chances of landing a fast trainer (high MV) from T players is high but its possible to get training duds (relatively speaking) too. You'd have a much better chance of determining a T players training rate if the Market Value was displayed. Whether T players are worth it for using depends on your Transfer Market competition and whether you have T but no cash. An Academy player costs High T, low cash whereas an equivalent TM player is high cash, low T (depending on competition) - thats before you consider the Q gap (if you are comparing it with 5* players).

Some players (presumably with limited time to generate cash in other ways) sign the T player in the expectation it will deliver more cash than Bank Loans. FAs are still the best cash for T generator but take more time.

The idea behind the Youth System is its an opportunity to sign a youngsters free from TM competition but its a high T cost. I just wish the Q ranged from 4-5*.

2. How big difference it is in-game between players with skills - for example - Q24 and Q29? For example, I have a GK with Q24 - will it be big improvement if I buy Q29 GK?

We don't know exactly how it works but its expected (from observation) that the difference is higher at lower levels ie a 5Q increase from 24Q has greater impact than a 5Q increase on an 94Q player. I call that the Absolute gain which delivers diminishing returns. The alternative would be a Relative Gain where Q is judged against a base level (say the 1* value) then impact would be similar across all levels.

3. What SA Shadow Striker gives? I mean, it boosts shooting or what?

Shooting afaik.

4. When merchandise/food stands on stadium give good profit? For now I have lvl 2 and I get like 500-700$ per game from it.

I don't know if it gives much relative value. Its another part of the mechanic that needs to be raised before you can raise other things I think. But so that you can do the comparison, my facilities are maxed out at level 15 and Merchandise so far this season has delivered just over 1/3 (66.3m) of ticket sales (185m).

5. Is there something I can do if I did an offer for tokens and I didn't receive them, besides writing a message through help section on sponsor's page? I sent quite a few of them and didn't even receive a reply...

Join the Club - check your browser settings for pop-up blockers, ad-blockers etc. Offers, use trackers to determine their completion.....particularly on mobile apps you can see the tracking browser windows opening.

Sorry if the above repeats other answers or contradicts them. 1. I've not read them and 2. its my opinion.