Here's what I've learned, but no first hand experience...
You can make a few bucks, especially on referigeration. But don't count on a good flow of income unless you want to keep at it full time.
If you keep at it full time, you risk the ire of local immigration authorities. It will be very difficult to get work permits. You can do some casual work under the table for other cruisers with little risk but if you go ashore, you will need work permits.
Good, well prepped steel is great. But you need to find good well prepped steel. There is a reason the vast majority of cruising boats are fiberglass. Easy to work with and quite durable. Just stay off the reefs.
All I've read on forward sonar is they don't work well, especially in shallow water where it's of most value.
You have some time, there is tons of info on the net. keep surfing and reading. You will learn a LOT.
Welcome to the asylum!