Not too sure about the bossing part lol; this is a plat free account, and I'm afraid I won't be able to participate much with any group activity later on (heh, I can't even teleport anywhere without having to either sell stuff first, or dump them!)
Hey Mariner. Have you not found out about leystone fragments yet? They are little stones that allow you to teleport to any leystone that you have discovered, even if you have more than 10 items in your pack.
There are a couple ways to get them.
1. Collect mining picks in Crookback and hand in to the guy at the entrance... I think you get 20 gold and a leystone fragment. You need four picks, which are found in little chests lying on the ground. They respawn relatively quickly, so run around Crook for about 30 mins collecting them, and you will end up with a few ley frags.
2. Buy them from players. I often shout that I am buying leystone fragments, and usually get some low levels willing to sell me some that they have collected. The fragments are also sold in the plat store, so some plat buyer might be willing to buy a bunch for you, that you could then buy with gold. I usually pay 10 to 20 gold for each fragment, depending on how desparate I am lol.
As for the bossing part, you don't necessarily need plat to join in boss fights. If you have some good Druids by your side, they can keep you alive. You can also buy idols from other players. You will need to join boss fights in order to get the drops, which are then used for getting Warden armour. .... that or you will have to farm a lot of gold to buy the discs.
And yes, you can teleport to the castle for free. I always teleport to the castle, then run out into Lir's/DC. Getting back to OW or whatever, I use a ley frag.