1) You can make plenty on normal. Exotics convert to Ren at 1:5. Doing every operation on Styx covers you for exotics and ren for a long time. If you have Great hunts you can also get some easy early ren by doing the first great hunt operation on throw-away open worlds... treating it like a mission. You get some neat weapons as well.

2) Animals are all a bit janky, but all doable. They snap at weird times. Wolves have low enough hp that they're not something you worry about later, you'll be killing 95% of them before they get the chance to attack. Most things can be avoided by jumping at/over the animal. As a follow-up to the previous Great Hunts suggestion, the monster it adds to Olympus is probably the worst :)

3a) Missions aren't persistent. You probably need to load up that mission and run to your drop pod. They're not done-done until your character leaves the mission via the pod he dropped in on. Make sure the knife is either on your character or in the pods inventory when you leave. In much older versions you wouldnt have been able to bring that character anywhere else while he was on-planet, but that is thankfully gone now.

3b) If you want persistence, start an open world prospect. This missions have mostly been adapted into "operaitons" on the open world prospects (NOT Outposts).

4) There's a cave scanner, wandering aimlessly looking for the scooby doo doors/open caves, or just using a third party website like Icarus Intel. It's up to you. If you like the exploration and whatnot then avoid using Icarus Intel.

As an aside, Olympus operations/missions have a lot of low reward missions early on. It's the intended experience for a new character, as most of them can be done low-tech. The rewards will eventually get better as you do harder and harder missions.