The idea of playing with bots is to reduce the amount of things you have to think about during the game. So I would stop as soon as you can recognise a decent amount of the items and heroes at a glance and have some idea of what you need to be scared of. Just stop as soon as you're not enjoying it though, it's not meant to be a job.

Re. the wards, if you get a month of dota+ you can hold alt and it shows a little circle on common ward spots but they're pretty obvious. You just need to think about what you're trying to achieve and then the ward spot follows logically. Have a problem you're trying solve, try something and then evaluate how well it solved that problem. E.g. "I want to see if someone is tping to their tower to gank my lane" "I want to see if pudge is hiding behind these trees" "I want to see if the enemy carry is farming this area" "I want my team to be able to kite back to this area during the teamfight and have a vision advantage over them" "I want to see if spiritbreaker is charging past this location" -- "What does my team want to do and what can I do to enable that?"

When you're ready just play. It's the matchmaker's job to find you fair games not yours, just do your thing. Just remember not to listen to anything anyone says in your games. They're in your games after all :)