I write this advice as someone who is very much into the points and miles game and currently hold 14 credit cards. I just got off the phone with Bank of America for about my 5th Alaska Visa application (see above post about great redemptions using Alaska miles for CX tickets).
While I do not recommend doing what I do unless you have a lot of organic spend, I simply state the above to point out that my advice comes from some experience with points and miles cards. A lot of people do cashback cards and that's great, but I like the high value redemptions on airline tickets and hotel stays.
I love the Chase Sapphire Reserve card for my purposes and I would recommend that except for the fact that it does not have the 100,000 point bonus any longer. It's a 50,000 point bonus for the $450 annual fee. The $300 travel credit is easy to get, but that still makes the annual fee $150 versus a free first year with the Sapphire Preferred card at the same 50,000 point level. Unless you are travelling on airlines a lot and can use the Priority Pass regularly that fee is probably not worth it. Get the Sapphire Preferred now and then downgrade it to a Freedom or Freedom Unlimited at the one year point. We can talk about using the points or transferring them out prior to the downgrade at a later time.
Some have said that the no annual fee 2% cards make more sense, while technically true that does not take into account the value of the initial bonus points. The beauty of the Sapphire Preferred is that you are getting a great stash of beginning points that are very versatile with no initial annual fee.
The loss of the cash discount is an issue it would seem, but maybe you can negotiate a little with the flight school by paying a little in advance since you have the cash. Even so the credit card points and miles game is all about arbitrage. The 50,000 points could be valued as high as $1050, but let's say minimum $625 if used on the Chase portal (lowest value). For the $4000 spend requirement you are out the flight school cash discount of $120. Worst case is you are still ahead by $505 with the credit card.
Don't keep using the card at the flight school after meeting that $4000 minimum spend though. Either go back to cash or get another card and another bonus whose value will again be higher than the 3% cash discount you are losing.
There is tons of information about this topic on Reddit (Churning); The Points Guy; and Doctor of Credit websites to name a few. If you start on the credit card points and miles game must reads are the R/Churning Wiki:
https://www.reddit.com/r/churning/wiki/index
The Basic Reading threads on the right side of that page for Beginner's Guide to Chase 5/24 and Credit card decision flow chart are very good.
