Should I learn Italian from Spanish or English?
Which should I start from?
Doing Spanish would give me practice in both languages, but I don't know as much Spanish as English, so I could get lost with words a few times.
Do it from Spanish. You are less likely to get the two languages confused that way, and you practice your Spanish. Plus it will prevent you from relying on English, you'll start going directly to Spanish. Yes, you will make more errors, but it's a great way to learn.
As far as I know the selected words of the different trees are mostly the same, so being you a level 25 in Spanish here in Duolingo, you shouldn't have many problems with your Spanish. Maybe you would go a little slower than if you took the Italian from English, but you would have the benefit of working two languages at the same time and I think it would be more fun.
I think it would be way easier studying Italian from Spanish because of their similarity, but if you are still studying Spanish you might get confused and end up mixing them. Anyway if you have a solid knowledge of Spanish I'd suggest you to study Italian from it since they have very similar vocabulary and their grammar is not that different either.