Woah! (I am on "dial up")
I would reccomend the styro trick. If you cover the styro in tape (multiple layers) the resin does not melt it.
Steel is often over rated. The learning curve is steep, and much scrap before perfection. Not that it would not be worth it, it might well. But I would weigh the: time, frustration, level of expectation, value/resale. and your ability to finish a possibly long project.
Remember to make your styro form about 1/4" shy of the level you desire. In an additive process it is much easier to add more resin or filler than it will be to remove it.