How to work with cryptocurrency?

Question

ASP.NET

Hello.
I want to write a service in which, after registering an account, there will be the following actions:

1. The user will have their own crypto wallets (I want to make at least BTC, DOGE, LTC, ETH)
   
2. One RUB USD wallet will appear
   
3. It will be possible to interact with cryptocurrency (transfer by address, replenish by address)
   
4. RUB USD replenishment withdrawal
   
5. Operations will be performed on the site after which the balance will change
   

1) I don’t see any problems with money (USD RUB) yet, I imagine some kind of implementation through the cash desk, but I don’t know how to interact with the crypt, so far I’ve only found the BlockChain API, DogeChain API, but I’m not entirely sure that this is the right way. Is it really necessary to work with each cryptocurrency using a separate API? Is there a free service that will make transfers without commissions?
2) The site will have a main wallet through which everything will go (the user made a purchase, money went to the site balance, sold - from the site to his balance). There will be many and often such operations, will I need to do each operation right away? (translations) It seems to me that they will be long, because they must be confirmed, but I need it to be visible that the action is completed and the balance has changed, how can I do this?
In short, I can explain everything like this. There will be a site with 1 on 1 games.
For example, a game of tic-tac-toe:
2 people place a bet of 1 DOGE - 2 DOGE come to the site's wallet, and their balances have changed.
The winner gets everything minus 0.01%

Answer 1

1) Are you sure about these services? Why won't they close tomorrow? that wallets will not merge? and to answer you, create it yourself, manually
2) In general, the operation is long, but technically not. See the status at https://etherscan.io for example, they have a good and free API
P.S. Regarding the first question, there are libraries that will allow you not to reinvent the wheel

Answer 2

See EtherAPI.net . All the bikes have already been made for you