More Words, Deeper Hole

ETA: I am not at all an expert in Patreon, so I second the recommendation to consult somebody who's done it before. That said, here's what makes sense to me.

If you do it by review, and charge $1 per, that's $2/week per subscriber, or $8/month (assuming this covers both your current review series). That's about in line with a monthly Spotify subscription, for instance (which is $10/month). If you get 100 subscribers, that's about $800/month. Price point is always tricky with these things; you want to make it low enough that lots of people are tempted, but high enough that it actually adds up to something.

Does Patreon support optional one-time donations? If so, that's how you could field review requests. Otherwise you could do it directly through Paypal.

If you do it by month, the tiers could be something like :

$3 - you get to read one set of reviews.
$5 - you get to read both.
$10 - extra content or the ability to nominate and vote on books to review, choose one.
$15 - extra content and the ability to nominate and vote on books to review.

I realize the second option depends on several unsolved technical issues. Maybe start with per-review, see how it goes, and then switch to the other?

ETA2: or you could just set a minimum, say $2/month, and promise little or nothing.