I'm still fairly new to R3E myself (got into it post FFB update) but happy to share experiences/advice. Firstly what's necessary to buy depends on whether you want to race online or offline. If offline, I suggest you just try the free content and then buy whatever takes your fancy as and when the mood strikes. If online then it's a bit more strategic and either you cherry-pick one car in each category you want to race and buy tracks as you go or get some packs.
I'm mostly interested in the historic stuff and ranked online. What I did was buy the Rookie pack and Legends pack first, then bought the European track pack during the recent sale, and just recently ended up buying premium anyway as I'm having such a blast.
In hindsight I should have just bought the premium straight away but frankly, I don't begrudge them the money as it's now my favourite sim. It's certainly a lot cheaper to bite the bullet from the get go if you think there's a chance you'll want to race online often. Hypothetically if you only bought one car in every category and all the major tracks it would cost you far more than just buying the lot in one go via the premium pack. If you buy VRP in Euros, it's significantly cheaper than buying the content directly in-game with money directly. There are numerous youtube videos and threads about this
The starter pack is pretty good if you don't want to commit too much but want some variety. With this, you are guaranteed at least one rookie ranked race server will be running content you own each week. Once you progress a bit you'll want to join in with some of the faster/more interesting middle tier racing and that's where you have to really decide what you enjoy and what you are willing to pay as invariably it'll be paywall stuff.
Unlike iracing there are usually only about 2 to 6 ranked races available that have a decent number of drivers at a time. This means I find I end up doing a lot more 'arrive and drive' stuff where the only practice I do is on the server in the practice and qualy sessions themselves. Consequently, it's good to know I've already got all the tracks and cars unlocked so that I can just join a server and get racing if a combination sounds like fun.
FWIW my favourite cars so far: Tatuus F4, FR3 (F3), DTM 1992s (all), DTM2016 (only tried the Merc), Touring Classics (all), Judd Hillclimb. In my opinion, R3E should now be the go-to sim for single-seaters and touring cars in particular, but it seems to do everything pretty well. The only car I didn't massively enjoy thus far was the GT1 Saleen, which might be because it's one of the few cars not updated from a very old tyre model. I'm also less interested in their GT3/GT4s as ACC does these so well.
Apparently, they have black Friday and summer sales (which recently ended).
Honestly, the ranked servers are just sensational fun. Almost every race I've had clean, side by side, respectful racing and even when there is minor contact, it's often survivable with neither party spinning out so the battles continue. The FFB is also so good that I find it's very rare that I can't react to catch and prevent a spin meaning I can safely learn new cars and tracks whilst racing online (just more slowly and further back in the pack). Polar opposite of iracing in both regards. The developers really do deserve every success.
