Yes you can do the tune-up yourself, you may need some tools from HF tools.
No you don't need a mechanic.
You will need a factory service manual, and probably need a little help from this forum to help you with your tuneup.
You shouldn't buy an outboard if your not going to do the maintance and fix it yourself, you need to know your motor and boat.
If you think boating is turn the key go boating, your in for a big disappointment pal.