Quick answer
Can anyone see my wallet balance?
Yes. What a public ledger reveals, and what it doesn't.
The long answer is still being written.
Other questions
Is USDT the same as Bitcoin?No — one tracks a dollar, the other floats. Who issues each, and why it matters.
What happens if I send to the wrong network?Usually the funds are unrecoverable. When they aren't, and what to check first.
Do I need a hardware wallet?Depends on the amount and how often you move it. A threshold you can apply.