It's not my definition, a spoiler is information that you'll get if you keep watching the anime, the answers to the other two quesitons will not, nothing changes if you finish the anime, they aren't touched upon later. I don't know why there's even a debate, just tell him every bit of info there is that you don't find that important then, if it's not spoiler for you, go on. Everything is part of the plot and relevant otherwise it wouldn't be there in the first place, you don't get to decide what matters and what not and even if you believe something is not that important, it's your own interpretation and you don't get to force it on others and ruin it for them because you think you can decide what's best for them. Keep it for yourself and let them experience the anime in every detail the way it is supposed to be