Most of the welded forks I've seen pinch in at the bottom so the star nut will be ruined by punching it through. The only ones that seem to be constant all the way are some of the older pressed in Marzzochi MTB forks. Check your own and measure it to see if pushing it through is possible. Too many variables to say either way without seeing it.

Yes, if you use a longer bolt you just need to tap or pry the bolt so the star nut kicks over a little and the bolt sits in line with the tube. There's enough play in the threads that as long as you get it close enough by eye it'll be fine.