I'm no expert, but here's the generic advice you're likely to get.
1. Color is determined by many things, but most notably the grains/extracts used combined with boil time. Adding more extracts at the beginning of the boil will create a darker wort in the end due to what are called maillard reactions (think white bread in a toaster). High heat combined with the barley sugars causes caramelization and darkens your product. Many of us dodged around this by just adding more of the extract later in the boil. Try adding half at the outset and half at about 15 minutes remaining (remove from heat to prevent scorching).
2. More BTU's means a faster boil, a more rapid boil, and in some cases better propane economy. If it is worth it to you to upgrade your burner for any of these purposes, go for it. I, personally, do all of my extracts and all-grain batches on my stovetop due to convenience and economy.
3. Yeast is the real rabbit-hole of the hobby. Lots of factors will affect the "yeast-flavor" in your beer. The easiest to control are yeast strain (some are valued for their yeast flavor character, others are considered "clean" or "neutral"), pitch rate (more yeast typically means less yeast flavor because of less cell reproduction - use mrmalty.com to find appropriate pitch rate), fermentation temperature (using the low end of the yeast temp range usually means it will turn out a cleaner flavor whereas high end of the temp range will enhance the ester-production of a given yeast strain increasing the overall yeast character), and dissolved oxygen in the wort (more is better - shake for 15 minutes, aerate with a stone/tank setup, etc).
Hope this stuff helps. We're all here to learn.