I want to build a blockchain wallet that works with BTC, ETH, and USDT, I understand that I must to run a server for bitcoin (bitcoin core) and ethereum (Ethereum Node) full nodes.
I have 2 questions now:
1- Has any full node for Tether?
2- Has it any benefit or danger that I will run 3 full nodes in one server?
You don't need to run another node for Tether you just need to connect to ETH and pass it's smart contract data from ethereum blockchain!
which you can see the smart contract here
Try Web3.js and Infura{it has free trial} and use testnet to experiment everything
about security the only thing that you should keep safe, is the private keys and backup mnemonics