Not everything needs to be an investment. It is ok to enjoy your property and do what you want with your house.
If you can afford the costs and the future expenses are within your budget, then go for it.
Metal garages require more upkeep and need to be properly insulated to be more than a shelter. Insulating them makes the interior upkeep harder. It’s a tradeoff.
What upkeep would be required on the interior? Not having a garage in the northeast sucks pretty hard, this would be my only option for a garage. I don’t have to get everything done asap either, looking to do things in chunks to not get totally overwhelmed mentally and financially
Its going to rust and if you don’t keep it painted, it’s going to rust even worse. If you insulate the inside, you won’t be able to treat the rust on the inside because it will be hidden.