I haven't played FIFA yet this year (because I tried PES and I'm pleasantly surprised with it) but I am a veteran of FUT and not spending any real money on it. Not the best player mind you, but have come to learn a few things about the game mode itself.
1. I would say use a "rest squad" to avoid having to use fitness cards. If you don't normally play squad battles, use a squad battles game here or there (you can play on an easier difficulty if you'd like) with your "rest" squad. Although I know you said you like to keep them at full 99. So you would have to play every other game with your rest squad and that could get tedious.
2. I would recommend doing bronze pack method to generate extra coins, and you can also save some of those +10 squad fitness cards you can get out of those packs to use if you'd like. Or the +20 individual fitness cards you can save those as well. Sell some of them on, keep ones you need.
Last year bronze packs you had a chance at getting a few silver cards, and you can't this year so profit may not be as much as before. But still a lot of those bronze players you pack are useful for SBCs. I still think there is pretty much no way you will lose coins in the long term by buying bronze packs for 400 coins and selling the stuff on. You should be able to keep fitness cards you need and STILL make plenty of profit because of how SBCs work. They players you can't sell you can save for future weeks, because a future SBC will come out where you can sell those players at some point almost guaranteed.
The problem is that you will have to spend time buying bronze packs and selling on the cards, but for me it was a better alternative
3. Others will be far better than myself to comment on this - but keep an eye on cheap team of the week cards that you think might be able to make profit on in following weeks. One mistake I made in the past was basically saving all my coins to wait and buy that one player I want. Which is still good, but requires more grinding, you may be able to make more profit by "investing" in cards that you can make future profit off of.
Also - use sites like FUTBIN and FUTHEAD to identify players. Those sites have roughly how much a player costs, and how much their value is increasing or decreasing on the FUT market. You can also see how chemistry styles impact their attributes and that type of thing. If you find the right player, having the right chemistry style on him is going to help you out. As for specific players, I would say the typical "sweaty" Premier League players are still good (although I have heard pace is nerfed this year). Look for players with high physical stats, that you may be able to boost other attributes with chemistry styles.