A lot of the plotters and printer will come with software. You can also download trial version of others to see if you like it. Many have switched to the subscription model to the cost of entry is much lower now. For $50 a month you can have access to all of Adobe's programs which is pretty nice.
As far as equipment goes, I would say be conservative at first and scale up once you are making a little money. Don't be afraid to reach out to some of the merchant members on here and see if they have any demo equipment they're willing to part with. They have deals all the time especially after a trade show. But I think that your doing it right with subbing most of out right now, make sure there's a market first.