I think you need to think specifically about your ds and his needs. Think about what's important to you as well, and ask a question that will show the persons views on that, without giving away your own opinion, iyswim. That way, you get an answer that comes from them, rather than them telling you what they think you want to hear.
I'm a 1:1 TA as well as a parent to a DS with ASD.
Personally, I think it's most important that they come with an open mind and are willing to learn from your DS, rather than thinking they are an expert in ASD and having a fixed view of what will work. So, do they understand that your DS is an individual and there will be a learning curve while they find out what strategies will suit him? Helpful if try have a raft of strategies to draw from, some from their own experience and some from you and the school, what has worked in the past. (Mixed metaphor? )
The huge meltdown one is a bit unfair, I think. I would have no idea how to deal with it until I knew what worked for your DS. Would he need to be left well alone somewhere safe with supervision, or to be held, or wrapped in a blanket or distracted or what? Better that the TA learns his triggers and tries to avoid them happening.