To be able to fast-travel to the castle from the start, you need to make it's map marker 'visible'. To do that, load the mod up in SSEdit, go down to "Worldspace" on the left, expand the sub-headings under that and hunt around until you find an entry that has the name of the Castle in it (every mod author does it a bit different). What you are looking for is the Map Marker entry, it will show up on the right pane. Once there, scroll down until you find the heading called "Map Marker". Expand that menu (if it isn't already), and find the "FNAM" sub-heading. In the right column next to that, double-click on that line and that should bring up a drop-down menu. Click the entries for "Visible" and "Can Travel To". As far as owning it from the start, IsharaMeridan is probably right, so while in SSEdit, go up to the "Activator" heading in the left pane, expand that menu, and see if you can find a activator that checks for gold in the player's inventory (not sure how it would actually be worded). Then edit the value in the right pane to 0 and you should be all set.