As I understand it, currently only Member+ really makes a big difference as you get access to Games+ with some significant content. It costs 750 coins, or a bit less with a discount. (Discounts are supposed to be a regular occurrence, but I haven't seen one yet.)
[Prestige 4, for 40,000 coins (again less with discount), is apparently the only other thing that makes some sense, as it gives access to AI generated images. It does not technically include Prestige 1-3, but it gives access to everything under Prestige 1-3, which is currently practically nothing. Therefore getting Prestige 1-3 really makes only very little sense. In other words, there is nothing worth getting in the price range between 750 coins and 40,000 coins. PS: I was talking in terms of access. I think the Prestige levels also allow you to customize your forum post, which I am not interested in myself.]
You get coins for forum activity or for putting your existing coins in the bank (Shop -> Bank), leaving them there for 24 hours without any further bank interaction, and then clicking a link to get 2% interest. This interest is in fractional coins, though it is rounded down for display. If you manage to click this link exactly every 24 hours and do not put any additional coins in the bank (which you should of course do, always immediately after getting the interest), it takes 35 days to double your bank balance. It would take a bit over half a year to get from your current 25 coins (assuming you have nothing else in the bank) to 750 coins that way. If you reply to my comment, it will be a little faster. Also, I am going to like your comment, and that should make it a little faster still. Any doubling of your initial capital reduces the required time by a month, and doubling 25 coins with forum activity is of course quite easy.
[If you want to get Prestige 4, consider not buying Member+ as soon as you can afford it. E.g., if you get interest for 750 coins 35 times, you have 1500 coins. Then you can buy Member+ for half of that and still have a starting capital of 750 coins that should allow you to reach Prestige 4 much faster. This is basically why I do not have Member+ yet.]