This is a common issue! Several factors can prevent solder from flowing correctly, including insufficient heat, dirty metal, incorrect flux application, or using the wrong solder for the job. Ensure your metal is clean, fluxed properly, and that you're applying consistent heat to the piece not directly to the solder itself.

Achieving a high polish requires thorough preparation. Start with progressively finer grits of sandpaper or abrasive pads to remove all scratches from previous steps. Don't skip grits! Once scratches are removed, use appropriate polishing compounds and buffs, ensuring each compound is completely removed before moving to the next. Cleanliness is key for a brilliant shine.

Warping often occurs due to uneven heating. Try to heat your entire piece gently and gradually, rather than focusing the flame on one spot.  Consider the thickness of your metal; thinner sections are more prone to warping.

Firescale, or cupric oxide, forms when copper alloys are heated in the presence of oxygen. To minimize it, use a good flux that protects the metal from oxidation. You can also pickle your piece frequently during heating cycles to remove surface oxides before they penetrate deeper.