Learning another language before fluency in English is not necessarily a bad thing. However, I would never advise a student to start a third language until at least an upper intermediate (B2) level in their first foreign language. I will mention two reasons why I suggest this.
First, when numerous languages are studied simultaneously it will take longer to solidly master grammar in either foreign language. As you learn a grammatical rule which is different from your native language, it will be easy to confuse whether the rule applies to English or Spanish. Your mind will constantly be thinking things such as, “I remember where the verb goes...but was that the rule for English or Spanish?” You will therefore make grammatical errors for longer in both foreign languages.
The second reason why I would recommend waiting is because of the learning your mind goes through when you are not studying. For example, if you study English for one hour a day, you are actually learning for longer than just one hour since your mind is continuing to learn in the background. Without realizing it, your mind is processing the information you are learning and making new connections. If, however, you are learning two languages at once, the “background learning” is divided between the two languages, minimizing the learning for both.
These two reasons are why I reached a fairly advanced level in German before I began learning Spanish. Though I personally waited until I was at a shaky C1 in German. (I am at a B2/C1 depending on a few factors).
If you told me that you would take a break from English to learn Spanish, I would still suggest waiting until an upper intermediate (B2) level before doing so. This is because if someone takes a long break in a language they know at an elementary level (A1-A2), after the break they will discover that they have forgotten a significant amount.
I hope this helps. :)