Now that you have seen a cacophony of diverging and converging opinions, I'm sure you are sure of the direction you are going to take. : ) Different experiences breed different opinions. I don't like to change languages if I don't have to. I started out with the UCSD p-System Pascal in college using an IBM TERAK machine, took a one semester FORTRAN class for engineering which used physical cards and batch printouts. FORTRAN and card reader debugging sucked and vowed never to do that again. Then I learned Apple BASIC on an Apple II. BASIC was not good for structured programming so I was happy when the UCSD p-system Pascal was available for it. However, I was not so happy with trying to swap 5 1/4 floppies in and out all the time when the TERAK had 8 inch floppies. Then Turbo Pascal came out which was very nice. The real milestone was seeing the 128 K Macintosh which made sense and computer designers who "got it." To add icing to the cake, one of the first Mac applications was Macintosh Pascal which in my opinion was the best programming environment for the next 20+ years. However, Jobs and Apple made a terrible mistake (haha) and decided to go with NextSTEP and a weird version of the C programming language called Objective C. In the meantime, I learned C for some embedded VME stuff had a nice affair with LISP and Prolog and OPs5 and CLIPS, then got tired of programming for a long time until someone resurrected the old Mac Pascal IDE to run on fairly modern Macs under Carbon. However, this was short lived and I migrated to FPC which is an open source version of the old (and current) Turbo Pascal. However, this was not optimal since all Apple's development interfaces was Objective-C and it was difficult having to do extra work to get things working. Then I decided to survey languages which were cross platform and decided to concentrate more on Python. It was not more than two months into this that Apple came out with Swift that I immediately ceased everything else and went Swift all the way. Since I had the advantage of not having to earn a living programming, I was able to take my time and learn Swift, not be too adversely affected by all the language changes, and also start really learning Apple's API's.
If you are going to concentrate on Mac development, drop Python and go Swift.
If you are new to programming and don't have to make a living coding, forget Objective-C and go Swift.
If you want to hack (nothing wrong with hacking) and/or make small programs for yourself learn Swift and the minimum API's for iOS or Mac OS.
If you are looking for a Mac Dev job, you must know Objective-C and the Mac API's. However, my guess is that the most fun and successful companies will want you to know Swift.
If you like Windows and that realm, I don't have any opinions!.
If you want to be a professional developer working with teams, you will want to know a lot of concepts, most are platform and language agnostic. I would say about 2 person years of tutorials and experience with multiple languages and platforms.
Object Oriented design patterns
Object Oriented Design
Agile Methodologies in general
Test Driven Development
JSON
SQL (and other) databases
<< I'm sure others can add a few more core knowledge skills >>
If you have gotten this far and have picked Swift as your language of choice, you will be glad to know that there is a plethora of books, written Tutorials and Video Tutorials on Swift and iOS software development as well as general software development skills. In fact there are too many tutorials and many of them are not so good and can even be confusing. To short circuit all the trial and error (which I have done already) go and get 1 month trial memberships to Lynda.com, Pluralsight.com and RayWenderlich.com. Don't get them at the same time but rather start Pluralsight after Lynda, etc. because you will not be able to get through all the tutorials in one month. In particular, view at least one tutorial by Simon Allardice on Swift or general programming. Very likely you will not mind paying for a paid subscription rather than wasting your time with You-Tube tutorials.
Even though I am 100% pro Swift and Swift syntax looks fairly simple, Swift is actually a very complex language once you get into it. You can learn to code simple things in playgrounds and make useful apps, but Swift is meant to be a production language and Apple needs to maintain compatibility with old API's while looking forward to doing new things with the language. It is also a language in flux at the moment. Version 3.0 will make some fairly major changes and it probably won't be finally stable until the 4.0 version. Even so, the core language is pretty stable and usually the changes Apple makes are well thought out and useful - i.e. fixing shortcomings.
Finally, I am wagering in 5 years Swift will be in the top 10 if not the top 5 languages in use especially now that it is open source.