Hey Scoopz, welcome to the Guild! First of all, have some rep for jumping right in with a map.
As for your questions:
1) You can post the picture as an attachment. If you 'go advanced' when making a post, you'll see 'Additional Options' below the main posting/text box. One of them is 'Attachments'. If you click 'Manage Attachments', it'll bring up a pop-up box where you can upload stuff as attachments. This has a couple benefits - not only does it avoid a huge picture right in the middle of your post, but the image is saved to the Guild server, so it's still viewable if Imageshack or whatever host site goes down.
2) That river is... yeah, pretty bad. Not hopeless though! You've already hit on what I think might be the best method for a map like this - lines of varying width.
3) I don't think the text size is an issue unless you plan on fleshing out the map a lot more. As it is now, the map is kind of empty, and the larger text helps offset that.
What you've got done on the forest looks good, but I'd experiment with a darker, less green color; the contrast between it and the parchment background is pretty high. The mountains look good; I like that method. Ditto on the seas/seacoast - that's cool.
One thing you might consider is curving the text for the 'Kingdom of Astavia'. All other regional names follow a curved path and to me it's a little jarring that that one doesn't as well. I like the choice of font though - legible, and pretty without being too cutesy.
Most importantly though, the map is intriguing. Already I want to know what's going on in the realm of the Vampire Lords. Based on 'The Frozen Forest', I'm guessing this is set in the northern latitudes, so maybe the Vampire Lords live in an arctic land of semi-permanent twilight?
Anyway, your map is perfectly serviceable as-is, but a few tweaks could really make it shine. Keep up the good work!