Studying 2/3 languages at one?

I have a habit of studying far too many languages at the same time, and from experience 3 is definitely doable, but certainly not always easy when 2 of them are beginner languages. Your French will likely have to go just into maintenance, but it sounds like you're at the same sort of level I am, and at this point I find it pretty impossible to forget so I wouldn't worry too much! Films and podcasts will be your best bet for that, since it can just be as casual viewing in an evening, and should help with your listening comprehension of native speakers too

I studied French and Spanish at the same time, technically both as beginner languages but I got better at French a lot faster, so it was more like learning Spanish with a prior knowledge of French. There is definitely a possibility of mixing the two up, but there is a lot of overlap so you can use that to your advantage (both in terms of grammar and guessing translations of words you don't know in Spanish but do know in French). I also found that I quite quickly learned how to tell if a word was French or Spanish, so I didn't mix them up in my speaking/writing much after a while. Essentially the "mixing up" works more to your advantage than anything once you get used to the sound and look of each language, since it aids comprehension but doesn't impact production of language much.

Your Arabic may have to fall a little by the wayside at times, such as around exams, but I think with your other two languages complementing each other you wouldn't have to abandon it completely. I've twice focused on 3 languages (1 B2ish and 2 near beginner), and it's significantly easier when two are similar. When I was doing French and beginners Japanese and German, I had to let one of the latter two slide quite often as it was just too much information, but when doing French and beginners Japanese and Spanish (I forgot all my Spanish after GCSE haha) it was much easier, since it was only 1 completely new writing and grammar system.

Basically, it's definitely possible, but make sure you're keeping an eye on things and prioritising for exams when necessary As long as you do the odd vocab revision or read a news article in the side-lined languages, they shouldn't deteriorate too much while you're focussing on others!

Nice to see another language enthusiast or "polyglot" here if you're one for using that term haha

I can speak 4 languages and am planning on doing 3 languages at uni (whilst studying Portuguese in my spare time, although I'm just practising it as opposed to "studying" it) and will probably pick up another one if one catches my interest so I believe I'm fairly knowledgeable on language learning.

Generally the most common advice in language learning is to focus on learning one language at a time and I personally agree with this. Learning 2 languages from scratch at the same time would generally be difficult to juggle. However, it is entirely subjective and down to the individual. Some people would struggle to learn 2 languages at once as language learning doesn't "click" with some people and they'd have to focus completely on one language at a time. The important thing is to ensure that studying two languages at once doesn't hinder your progress in each one because it's generally better to speak one language to professional fluency rather than two language sloppily.

However, as I previously said, it's down to you so if you feel like you can learn 2 languages at once then go for it Your plan sounds structured and relatively solid. Arabic is obviously a very difficult language so that'd require a huge amount of work and concentration whereas Spanish should be a breeze in comparison for especially as you know French to a B2 level and even English shares a fair amount of vocabulary with Spanish. In addition to this, Spanish grammar is pretty easy and very similar to French so I don't think Spanish would be too hard for you to learn at all.

Regarding your worry about mixing French and Spanish, it is true that two languages being in the same language family can be both advantageous and disadvantageous as they're similar which makes learning the other easier yet their similarities may create some confusion. However, generally the better you know a language the less likely you are to mix it with another. I did what you did but the other way round as I learned Spanish and then French (and Portuguese very later on) and initially that did cause me to mix those languages together but the more I progressed in each language the more I was able to identify their unique individualities despite being in the same language family and now I no longer mix those languages together.

I'm aware that I've written a fair amount but the one piece of advice I'd recommend you consider is: if you think you'd be capable of learning 2 languages together without hindering your progress in each language then go for it. Only you know your mind and whether or not you'd be able to do this.

Viel Glück and I hope to have been able to help