Question first - what is your background? Do you have any real estate or title experience at all? That will answer your question...if you have no experience at all, and have never seen the documents involved in a mortgage loan, then I feel a certification course will be key to helping you understand what you're doing. Just be careful what course you choose - especially if you have NO experience at all with mortgages - you need to find the course that is going to go through all the docs with you. If I were in your shoes I would check into Notary2Pro (Carol reads here and posts occasionally) - it's my understanding her course is very comprehensive and detailed and, further, she provides post-certification support. I have not personally taken it but I hear good things about it - I'm thinking of getting back into some signings in 2017 and have tossed around taking her course to update myself on changes I've missed. But one thing - please - IGNORE YOUTUBE!
Most companies strictly require the background check - and it's good for your profile that people see you've cleared one. The check done by the State of Florida is superficial at best - another gives a second level of comfort. The certification will do the same thing.
As for the E&O - that's your decision based on your own situation. I used to carry $100k because I have assets; when I stopped doing loan signings I dropped it to $25k for as I'm now only doing general notary work. Just remember, standard E&O will only cover you for notarial errors - it will not cover errors you make with regard to loan signings. There IS Signing Agent insurance available but it's pricey.
Printer, well, you say you have no cash on hand but you need a laser printer - that's mandatory. So, I would suggest checking ebay and see if you can find a deal on a brother laser - I personally prefer HP, but Brother is cheaper - just get something to get you started til you can make some money. When shopping ebay just pay attention to page count and monthly duty cycle. I got a nice HP 4300 dual-tray in 2013 for $200 (and that included shipping) - that machine is still chugging along.
I will not comment on the NNA or AAN - well, yes I will. I initially got certified through NNA despite having a 25 year career as a real estate paralegal because I thought it would help - it honestly didn't. AAN?? I have NEVER gotten an assignment through them - they are very nice but I have been very disappointed in my membership there - I get no emails or updates or anything - and they especially do not provide a conduit for work. List here, Notary Rotary, 123Notary and any other free site you can. Get a free website - webs.com has them and there are others with which I'm not familiar. Set up a FB page and use that...these are all FREE..
Main thing? Make sure you have your notary laws down cold before you do this - there is no forgiveness for a notary who does not know his laws. Roger Rill in Ohio said it best - "you need to be an outstanding notary before you can be a good signing agent"
Good luck to you.