I also got into Transformers with G1, way back in the mid 80's, and started buying the comic from issue 1.
I had an off period during the Beast War era up until RiD 2000, when I was already an adult and started collecting them again, now having probably in the hundreds.
One thing you should know is that TF collecting requires quite a bit of space and disposable money. If you're OK with that, there are a metric ton of places where to start, but primarily there is two avenues: the Generations/Universe/Combiner Wars brand, and Masterpieces. I personally like the former better, as they offer a huge selection of characters and molds, are usually more pleasant to transform, and the smaller scale makes the great engineering stand out more. I only own one Masterpiece in fact, MP-01.
Regarding where to start within Generations, I would actually try to go for the older stuff that's not entirely sold out already or being sold for scalper prices, as this is probably your last chance to get it. If you can get your hands on the
Reveal the Shield Rodimus vs Cyclonus pack, those are two of the best molds in the series in their best color schemes and look amazing in both modes. It also comes with a Matrix and a Targetmaster.
Aside from that, we were recently graced with an actual
Arcee after thirty damn years, so you might want to hold into one in case it takes them another 30 years to release a new one
. I see it's already climbing in price, you should try to pay no more than 20$ for it.
Oh, we also recently got what to me is
the best Megatron in the entire history of Transformers. This should set you back 50$ but IMHO it's entirely worth it. Be careful not to get Armada Megatron instead as it's a slight remold-recolor of it but probably of no interest to a G1 fan.
Two more recommendations:
1) If you still haven't, familiarize yourself with the size designations and price points (Legend, Deluxe, Voyager and Leader especially) to know what you are getting and whether it's a fair price or not.
2) If you are looking for specific characters, feel free to post who they are here so we can give you pointers towards what representations of that character are available and which ones we think are the best.