Red Dead Online is good game either solo or with friends. The actual content includes free roaming quests, events, jobs and PVP sessions.

The most important currency is gold that you can unlock by exchanging your time (Or if you want, you can use real money but you don't need to.) to purchased most of the interesting content (Bounty Hunter License, Trader/Collector/Naturalist Role and Moonshine Building). Gold is also used to customize Guns (almost exclusively with it) or Outfits (which are purchasable with in-game dollars for most of the good ones). Use it wisely don't focus too much on customisation in your first hours.

If you play with friends, you will certainly enjoy the base content. If one of your friend has access to later content you can play anything with them even if you will not get the job experience for it until you get the job yourself.

If you play alone focus on doing the «Main Quests» and try to join people on the RDRO Discord to build the first gold you'll need to access the first job. After a while you will have access to more jobs and you will enjoy a little more your time alone. Focus on doing your daily quests to get the little boost of gold each day and also use your Gold Treasure Maps.

---

Edit: After 100h of gameplay, all jobs are unlocked and also the 40 Gold Bars battle pass.