As a child gravitating to another toyline / cartoon (like we all did) it was somewhere during season 3/4. I'll never forget getting a bunch of Headmasters and Targetmasters one Christmas. As an adult (and therefore a fan / eventual collector) it was somewhere during 2006, I was doing random word searches into Youtube and came across Dyansis' videos. Here was a guy who knew the character and bio backgrounds extensively, I was hooked and couldn't soak in the information quick enough.
Pretty quickly. But what really cemented it was when my wife bought me the Legends Optimus and Megatron from the first movie because she knew I'd liked them as a kid. As much as they weren't the greatest piece of engineering a spark (no pun intended) was lit inside me and I decided I had to have more. Alternators Ravage and a reissue of G1 Soundwave quickly followed, old toys were rescued from my parent's loft and the size of the collection snowballed.
If you''re getting back into the franchise from childhood then check online for toys of characters you were a fan of. In terms of series I'd say go for the most recent. Chances are the toys will still be out there or at least easy to come across online. For comics being a continuity nut I always think returning to the beginning of IDW (the ations) is the way to go. That said I'm aware that's a lot of content to get from so I'd advise going back to the last jumping on point which in this case is the amazing MTMTE and RID (now simply named Transformers). Both are so well created that you can't go wrong with them. But for a much greater understanding of the world do go back and check out the older stories.
4. What advice would you give to someone to get them into Transformers?
Exercise caution. It's a great hobby to get into but don't insane thinking you have to own everything right now. The last thing you want is getting into serious debt because you couldn't choose which of the 3 uber rare bots to buy this month. Because that was a bit of a downer piece of advice I'll give another. Join a forum or group online and make some friends within the community. From a personal standpoint I don't think you can go wrong with the TFYCC on Facebook. Introduce yourself, have some good banter and if you have the funds go along to a meet-up or convention. 5. Name your highlights of the franchise and fandom. Making and meeting amazing friends. Having this hobby is fun but it wouldn't be half as enjoyable without people to share it with. Talking online with and meeting them at things like Auto Assembly has been one of the happiest things to happen in my adult life.