Never buy packs with coins. Personally I'd never buy them with real money either but some do.
You can get so many free packs just from playing the game. Squad battle rewards, Rivals rewards, season objectives, FUT Champions (if you qualify), and Squad Building Challenges.
Generally speaking the packs are pretty terrible unless you get lucky. I've done pretty much every SBC, objective and gotten rewards every week and my best packed item was untradable 87 Insigne who was worth about 70k at the time.
The market is so low right now that you should be able to buy a good starting 11 of 2nd tier players with 1 week of rewards even with crap in the packs.
For instance you can get Havertz and Werner, who were my starting front 2 for a while for around 20k for the pair now.