[hashhar]

First things first. Set up a VM with Arch Linux, Slackware, Gentoo or if you are feeling adventurous Linux From Scratch. It'll go a long way to help you learn how Linux systems work. (Don't install a graphical environment, plain X server is OK though).

Now to your original question:

If you want bleeding edge packages go with either Arch Linux, Gentoo, openSUSE or Solus. I haven't used openSUSE as extensively I'd like to but haven't had any issues with it yet. The package format is a bit too much if you want to create your own packages though. openSUSE ticks all the marks in your checklist too.

Other than that I will suggest to keep your local dev environment as close to production as SANELY possible. Fedora and openSUSE are good bets.

Personally for rolling releases I've found Arch Linux to be the best (not because they are rolling release but because they generally keep the packages without any modifications from upstream). There is a huge selection of packages. But it suffers with the problem that it's not used in production and hence some issues can't be caught on it.

[Jonathanks]

I mentioned that stability is a concern for me. Don't you think Arch Linux feeding packages from upstream might not be ideal for me? That's the reason I highlighted Debian testing instead of Debian unstable.

I've used Slackware before, and it was an easy look into the system; except that package management is a bit stressful on Slackware, and its packages are not so up-to-date.

I'm running a VM with FreeBSD now; how suitable it can be for a laptop, I don't know yet. Battery life matters there too.

Fedora looks good; I already have a Fedora 24 disc, so I might go from there instead of Slackware. openSUSE tumbleweed looks great too. I'll probably try it.

[hashhar]

I haven't used FreeBSD on laptops. openSUSE is the best best for you I'd say. It's stable enough, had very good package repositories and is used by quite a lot of people. Fedora has the same issues regarding up to date packages.

I can't vouch for the package breakages on any system other than Fedora. I've just had a single package breakage on Arch in over a year. It was fixed by simply moving a file and making a symlink.