i have a patreon, and i do not do on-request rewards. admittedly, my patreon isnt great, but i dont think its necessary to do on-request rewards, particularly for any tier below $20.
the most important piece of advice ive heard about patreon for artists is make rewards out of what youre already doing. you have a script, you have sketches, thumbnails, drafts. do you have a buffer? you already have plenty of things to put on a patreon. for a leeeeeeeettle more work, you can post speeddraws (just record yourself drawing a page, and speed it up) or you could do sketchbook videos (dont put these on any tier lower than $15 unless youre lit just flipping through with your phone camera, theyre effort so theyre money)
if you look around and have a brainstorm, youll likely find a great many things you can already post to patreon, and a great many more that wouldnt be hard. monthly evaluations? sharing your tapas statistics each month is one ive seen around the place. you could look into offering private livestreams - if not technically private, just dont tell anyone else theyre happening - which is just a lil company while you work. vlogs and status updates are actually really valuable - many people come to patreon for behind the scenes information, to get to know the creator a little.
also, if you have a buffer, you can do early release on patreon. people loooove early release. dont base your entire thing on it, but definitely feature it, on the $1-3 tier (i know some ppl that give you earlier and earlier release the more you pay, but then things get complicated)
this all said, patreon will always be a eensy little bit of a tip jar, especially for webcomic artists. the people who pledge arent just doing it because they like what youre selling, but because they have a love for your work and want to nurture it. so yeah, your $1 tier can be little more than a tip jar. although personally, id set up a ko-fi for that.
dont quit your job, of course, but do start a patreon. it can fail for the first six months, who cares - ask your mates to pledge maybe, so it looks good. patreon encourages you to do that, actually - when i first started, i had several mates and my dad pledging to me. you can also pledge to yourself, but youll be about 40 cents out of pocket each month for VAT and transfer costs. youll find though that patreon really wants you to succeed, so they provide lots of tips that are genuinely helpful, you can take your own time following them. God knows im yet to do most of them.