I suggest to start with learning the tones. Learn to read pinyin.

What do you mean with ‘learning Mandarin’?
Do you mean learning to read and understand Mandarin? Or do you want to learn to write Mandarin?
Or comprehensive listening? Or speaking?
Learning to speak Mandarin costs considerably less time then all the other skills.

If you want to learn characters I wouldn’t learn more than 200 in the beginning. No point in learning more if you can’t read it aloud in context fluently imo. So, also learn frequent words that have those 200 chars in it.