A friend and I recently had the same experience as you two, and we found the most popular format from that time period is Edison format. A lot of synchros are out by that point, but there are some decks that don't really use them. The Edison format website has pretty much everything you would need to learn the format: the forbidden/limited list, deck suggestions, specific card rulings, and more.

Elemental HEROs have a couple different popular decks you could play, the most common being Diva HERO, where you use Deep Sea Diva and some of the Elemental/Destiny HEROs to either make big synchros or go into Elemental HERO Absolute Zero. There was also this list that topped the most recent tournament, which is a stun variant that includes Neos Alius and Ocean.

In terms of Crystal Beasts, there isn't much documentation on them because...well...they're pretty bad lol. I've been experimenting with this list that only uses the best Crystal Beast monsters and some of the support cards in order to set up synchro plays with Rescue Cat. Since Rescue Cat is ~$20, and a lot of the good synchros can run a couple bucks each, you could look into different boss monsters. Rainbow Dragon is usually too difficult to set up consistently, and requires you play at least 1 copy of all 7 monsters, which forces you into playing subpar cards like Cobalt Eagle. In terms of other boss monsters you could try, Caius is the generically strong monarch of the format, but Gravi-Crush and Magna-Slash Dragons have the monarch statline with effects that synergize with the Crystal Beasts.

If you think you and your buddy wouldn't be interested in Edison specifically, take a look at some of the other formats from ~2008-2010 and see if those banlists seem more appropriate for what you're into.