Welcome to RDR2O partner !
My few cents to You:
1. I would recommend "playing the game" for ranking up - there are some methods to XP "fast" like one mentioned above (shooting del lobos in thieves landing) but i dont reccomend them. They are booooooooring and dull. The best way is to just play the game, enjoy and learn the world (its a bit diffrent than story mode), hunt, make stranger missions, co - op story missions, some pvp, daily acheivements. Use better ammo on enemies for more xp. There will be achievements for playing like skinning 1000 animals etc, the moment you get gold buckle for completing one of these make sure to reset the achievement to get gold bars and start making it again for nice XP boost. You can reset most of them 10 times. Shoot every animal you come across you dont need to skin them all but its free xp.
2. For money making - best way is to hunt. Birds are good money, some fish as well. I personally hunt every type of animal until im full on my inventory and then turn back the goods. Dont spend money on cosmetics in the beggining. Buy Varmint rifle, lancaster reapeter and bolt action and reapeter shotgun first and upgrade them. Buy a good horse and saddle for gold bars. Use varmint for small animals and birds and bolt for everything else. Lancaster is good in missions and mid range pvp. BUY ABILITY CARDS FIRST then everything else - You dont need all ability cards but some are essental like : Paint it black, peak condition, cold blooded or stranger medicine, unblinking eye, slippery bastard, winning streak, slow and steady, horseman. I personally have all of cards maxed out but there are a few that dont matter at the moment.
3. Dont shoot ppl in free roam without a reason or you will get ur @ss handed to You by a high lvl. If you feel harassed or griefed just change sessions or go into co op mission etc.
4. If someone shoots at you shoot back
5. If you dont like playing solo i would suggest to posse up.
Hope it helps in anyway. Good luck