Self-assessment bottom basics

Hi all, sorry for the complete ignorance, but I've been working on a very limited self-employed basis as an income topper since 1st October 2018. I've just left my job because of health, and need to really step up operations. I registered as self-employed last year, but am I right in thinking that the self-assessment form due in Jan 2020 will cover earnings from Apr 2018 to Mar 2019? And that earnings made from Apr 2019 won't be filed until in 2021?

Also, I will be doing two types of self-employed work: sessional therapy work, which is fairly low level, and consultancy in my previous professional field, which will hopefully provide the meat of my income.
The basic sweep I've done on this suggests that it's one self-assessment form but recording 2 business operations? Both are just under my own name.

Should I have separate bank accounts for these, even though one is really minimal income per week?

I've signed on a basic tax course with my local authority - but this forum has always been helpful!

Thanks for reading this, and for any replies. It's all a bit daunting!