229,
Unless you drain to manage your CYA buildup you have to do this before you switch to salt and you will need to balance your water using TFP methods for the best cell life. Do you have a recommended test kit? If so, please post a current set of test results and we'll make recommendations to help you get ready. If not you will need to get one so you can make sure you are balanced for max cell life. Here are answers to your questions:
1. Salt system prices have gone up a lot this year; most people speculate it's due to covid and rare metal supply shortages. So it's hard to predict what will happen on pricing this winter. But I wouldn't see any harm in waiting a few months. You should buy a unit sized for a 40K gallon pool. Check the lb chlorine production for a fair comparison though since some brands are claiming they can treat a bigger pool than others with a given chlorine production rate.
2. Just looking at price for the unit can be a little deceptive. When you compare pricing I would look at $/lb chlorine production, warranty, and reputation for customer service on this site. Warranty is more important for salt systems because all brands have a few failures after year 1. Out of warranty this would be an expensive repair. Check out
this website for comparison information. I used this method and it led me to Circupool. They usually have some kind of sale to upgrade to the next higher production unit for a small price like $50. I ended up with an RJ 30 plus for my pool. I'm in year 2 with it and very happy with its performance. I use TFP methods to balance water and I think this helps a LOT for cell life.
3. Certainly you will see little or no cost for liquid chlorine or tablets after you switch. I also added borates and my acid consumption is way less than before the switch to salt. I think the payout for salt pools based on chemical cost is about break even after 5-6 years. But the real benefit is that it makes pool care much easier. I rarely have to do anything other than just run my FC, CC, pH tests a couple times per week and add about 32 oz of acid once per week. No more jug lugging. The other benefit is the water is much "softer feeling". My wife loves it and our grand kids say it doesn't irritate their eyes like other pools.
In addition to your TFP recommended test kit such as a TF-100 you'll need a K1766 salt test. It's the best way by far to test for salt. Test strips are only +/- 500 ppm accurate and this is not sufficient to manage your salt level for max cell life. You don't actually consume salt but you will lose salt when you drain/refill due to rain. I get a LOT of rain so I lose two+ bags per year due to this. I use Diamond Brand water softener salt from HD or Lowes. It's way cheaper than Morton's Pool salt and works fine based on my experience and other experts recommendations here. Just stay away from any brand that has additives for iron control or any other additives.
I hope this helps.
Chris