Hi Zandy, I started out playing rhythm guitar late 1970's and when the lead guitarist left in 1980 had to step up to the plate for some of that action. Needless to say most of the solos were short and not so sweet. Fast forward a couple more years and due to being unable to find a compatible Bass player thought I would give it a go, as hey, it's only 4 strings, how hard can that be? Wow, massive understatement as once you start listening to those parts in songs you begin to realise there is a lot more going on than just playing root notes.

Hardest part is your left hand action where playing on finger tips as you do on guitar will hurt like hell for quite a while due to the thicker gauged strings. Being on the shorter side and having a smaller hand as a result, playing in key of G or F is a huge stretch which is where I learned to use the flat fingerprint part of my fingers to fret the strings rather than tips which is what I revert to when playing guitar. If you know your scales it makes things a lot easier as everything is in patterns across the strings. Same deal on a Fiver which I reckon is better if you do play a fair bit between E & A as you can jump up a string to lessen the stretch as you get nearer to the nut. Pink Floyd's Money is easier to play on a fiver than on standard 4 stringer all because of being able to shift everything up to 7th fret for root B note on E string rather than 2nd fret on A string as there is a low G note to be played that is slightly off the beat too.

Right hand style comes down to what you feel comfortable with and how much effort you are prepared to put in with practicing. I am more comfortable with a pick as that is where I started out on guitar nearly 40 years ago but have got better with fingers over past few years but really suck at Slap and will have to spend a lot of time and effort perfecting that style. Big tip if you plan to use a pick, I have always used Jim Dunlop Nylon 0.73mm or 1.00mm ones as they don't produce as much of the 'click' that a harder pick produces and thus sound a bit softer. In fact my preference is 0.73mm as there is lots of flex that helps in many different ways and yet still allows for fast picking too.

Lessons.....Scotts Bass Lessons as Woks mentioned are good. I have subscribed to his Youtube videos but yet to find time to seriously sit down and learn some of the things he teaches. There is so much more out there on Youtube but this guy is entertaining and not too over the top. Don't fall into the trap of trying to read tabs or charts as that will dampen your enthusiasm as quick as anything. Bass is all about feel and groove, and ultimately keeping perfect time, things you probably already possess.

A decent cheap Bass from fleabay, gumtree, or crime converters for less than $100 may be hard to find and reckon these kits on PBG site would be better way to go...
https://www.pitbullguitars.com/shop/...ss-guitar-kit/
https://www.pitbullguitars.com/shop/...-kit-ash-body/
https://www.pitbullguitars.com/shop/...ss-guitar-kit/

Good luck buddy. You won't regret it plus you can still pick up your guitar any time too.

Cheers, Waz