Next, I am 6'4" and had a terrible time standing.
You're getting some good advice, but remember there is a whole lot more to riding than simply learning how to ride standing , with elbows up, etc.,etc.
First, note the 6'4" thing. My bike, since my height is an inch taller than that, has the high seat, lowered pegs(LOVE those FastWay F5's), taller bar, and all really help.
However, to make my bike feel like Shane Watts's bike does to him, who is always preaching stand,stand,stand my bars would have to have a rise of 11 inches ! Now that aint happening.
Also, there are a lot of riders who are known for having very effective sitting riding styles, as in sitting more than whatever the cutrrent trend is. One was Roger DeCoster (!), another Brad Lackey, another , from more modern times is guess who ? Another 6'4" rider, David Knight, who you will also find frequently riding with his elbows down (gasp!)
Sure there are lots of times it's better to stand,where we need to be standing, my point is it isn't the only answer/ the only style any more than the myth of "elbows up" providing more control and better feel for all riders.
My advice is get as fit as posible, ride as much as possible, and work on being as smooth as possible at all times. Wtch the pros rip through the tight stuff..their motors aren't screaming, they sound like they are in the classic 'gear high' mode whether on two stroke or four stroke bikes.
For woods racing a steeering stabilzer is mandatory, a Rekluse is not.... unless you ever run a Hare Scramble with one.
Good luck ! Doug