starting my first garden at a lower elevation

I grew up in the mountains so my childhood garden was at over 7500 feet. My new garden is down around 6000 ft. Is my growing season going to be noticeably longer? Will I have larger plants with the decreased elevation?

I have a 15 ft x 4 ft plot that's currently a mess of weeds. I've got plans to yank as many weeds as I can, acquire some horse manure-based compost, and rotatill the crap out of it. Any general tips with that?