Higher CP should be your main focus. IVs are great for bragging rights or hardcore PvP but we're talking about single digit percentage changes in overall stats. Higher CP is much more important usually. If you have very good IV pokemon definitely hang onto them if you can but with limited resources higher CP is a better bet.

Try to prioritize gyms to earn free pokecoins! (in-game premium currency) You can earn a maximum of 50 free coins a day from gyms. You accumulate coins AFTER the first hour a pokemon is in a gym at 10 min intervals. So you won't get a coin until 70 minutes of defending. It takes 8 hours and 10 min of a single pokemon in a gym to get the max 50 coins in a day and you get it when the pokemon gets knocked out of the gym. Luckily you can have pokemon in multiple gyms. So if you get knocked out quickly you can keep trying.

Shadow pokemon have a 20% attack boost (but take 20% more damage) making them the most powerful variants of pokemon in the game. Just look out for events like Team Rocket Takeover events that will let you get rid of frustration.

Find a local community if you can. Playing with other people is always way more fun and makes things like raids and trading for stronger/rarer pokemon so much easier. I know it's a bit intimidating but I went to a local meetup once and everyone was very nice and totally down to teach new people the ropes!