Obviously, I’m a huge Ghost fan, but here’s some information that may help you.
Ghost supports multiple newsletters (which sounds like your need to customize newsletter distribution). There’s not a built-in way for a user to pick topics to receive in a combined newsletter, but you could run multiple newsletters each covering different topics and let users pick which one(s) to receive.
Ghost uses Mailgun for newsletters. There’s support for importing a mailing list into Ghost, but you’ll definitely want to talk to the Ghost Pro team (if you’re hosting there) before sending to your 75k mailing list. [A former client importing 10k new subscribers needed to reassure them that his addresses were double opt-in.] Newsletters are somewhat customizable, but not completely. You can’t rewrite the newsletter template unless you’re self hosting.
There’s no scheduled email drip for new users built in, but you can add a third party that does this. (Some users also use a third party bulk emailer for newsletter sending.)
Restricting web content (and/or newsletters) to registered users (members) or to paying members, or members on a specific paid plan is all possible with Ghost. Ghost uses Stripe subscriptions for this. Ghost does not natively support one-time payments for content, gift subscriptions, or individual article sales. Outpost has some of those, or you could ‘roll your own’. (ref: https://outpost.pub/ )
If by ‘marketplace’, you mean that users (not trusted staff users, but regular website visitors) can add content or listings and sell things, Ghost doesn’t support that natively. (You could certainly have a form that allows users to submit a new marketplace listing and use a human editor or write a cloud function to post that submitted content, but you’d need to sanitize submissions somehow.)
Ghost doesn’t really include an editorial workflow. You can have staff users who can create posts (which will be your main content type) but not publish them, but there’s not a full approval workflow. If you have a whole editorial team, they might want to track their editorial workflow elsewhere. (A small team could use tags to indicate a draft post’s workflow status (i.e. #needs-approval #needs-revision #ready-to-schedule). There’s not support for on-post commenting, although you could use something like hypothes.is for that.
Ghost lets website visitors/members (not staff) log in by way of a magic link. That’s the only built-in option. They enter their email address and then click the link that arrives in email. Once they click the link, they get a long-duration cookie. (They don’t have to do this for every visit!)
I hope that’s helpful! Post again if you want more input.
If you haven’t yet played with Ghost, I recommend signing up for the free trial and kicking the tires – hard – for two weeks. There’s a LOT to like in terms of blogging/news/newsletters.