I think you have to seriously consider which is more important to you, longevity and power or size.
Bottom line is that with either 13’ 11’ 15’ you are paying for what you get, no more, no less.
With the 11’ you lose the High Res Display, which maybe not a deal breaker now, but in 3 or 4 years it’ll be antiquated.
With the 13’ retina, sure its heavier and 1 inch all round bigger, but is designed for high CPU tasks like audio and video production.
Honestly I would not touch a 128 HDD, regardless of which computer you choose its very easy to fill up with day to day stuff and will require constant monitoring/backing up to check you aren’t running out of space, again, I’dgo with a bare minimum of 256 if this is going to be your Main Machine.
I would NOT recommend a non-retina 13’ (I have one) and the screen is really starting to show its age with everything from HD movies to websites, I can’t imagine how it would feel in a year or two. Sure its upgradeable to a point, but the processor and GPU are year+ old technology and cannot be upgraded - pointless purchase IMHO. Once you are finished upgrading to an SSD / Ram you are going to be hitting the 1.4k mark anyhow and still lacking a higher res display.
Any reason you did not mention a 13’ Air ? There has been a few popping up on the mac Refurb Shop for around $1299 with the i7/256/8gb… Theres one at the Moment with an i7/512/8gb for $1550 which is not a bad deal considering the price of SSD.
The 11’ is a tidy little machine, has enough Power to run the majority of Applications out there pretty well … but then again my Lenovo s10 ran Traktor pretty well too. But i would not consider using it as my “DJ” machine just because it worked - it simply was not comfortable in day to day use.
You’ve already used an 11’ for day to day work, so I’m guessing you already convinced yourself that it’s “just what you need”. Well trust me when I say when you try a 13’ retina for a few days you will seriously be wondering how the hell you managed to work on an 11’ ever before.