Dude, I applaud you on going for the metal.
I must agree with the others in saying that adding resin wont do you any good with regards to adding strength.
What gauge metal are you using by chance?
Deputy Dog's suggestion of building a paper model first is a good one. that way, not only are you able to size the pieces more easily before hand, but the individual pep sections should be able to be used as templates for cutting your metal.
But yeah, based on what others have been saying, your best bet may be to grind down the welds and go from there.
[SAFETY]
If you're planning on using this to take hits, make sure you have some serious padding on the inside. Even with a properly built helmet (motorcycle, football, combat) it is still possible to receive head and brain trauma from a blow.
[/SAFETY]
As for the hyabusa spike, I'm having a hard time picturing it (mostly because my brain is a bit mushy right now
) but if that's something you think may be cool, i'd say go for it.
Keep up the good work and as someone who also looks to build a metal ODST set, I look forward to updates!