****WHOOPS: Just noticed this is the 13" model, not the 15". Caveat to what I say... the 13" battery disconnection is a bit more complicated than the 15". There are 3 screws attaching the battery to the logic board, AND a small chip that you can readily damage. So take a look at the SSD replacment (MacBook Pro 13" Retina Display Early 2013 SSD Replacement) before doing any of this. If you aren't comfortable with it, OWC will let you send them the macbook pro and they'll do it for you. Just a thought...
Before I answer, there is a problem with Dan's suggestion. Technically speaking, the external shell from OWC isn't supposed to be used with the OWC SSD. They don't specify why (and I haven't looked at the specs close enough to discern the reason - could be an amperage/volt or SSD component issue), but they prohibit you from putting the OWC drive into the shell. The Envoy Pro shell is meant for the old Apple SSD ONLY. This is my learning lesson for you. When I bought my first OWC retina drive when they first came out... I put it in the shell to do exactly what Dan is suggesting. The problem: the shell shorted the new SSD within 10 minutes. I had to send it back and get a replacement. Lesson? Do not use Dan's suggestion. It may cost you a drive, or at the very least, a delay to get a replacement. And they will ask you if you put the new drive in the shell... LOL. It may not happen, but I wouldn't chance it. Learn from my mistake. READ DIRECTIONS. Hahaha
(Moving on with my answers)
1. Backing up to Time capsule and restoring... isn't affected by the new drive's size, provided the new drive isn't smaller than the amount of data saved (ie, you backed up a 512gb SSD with 400GB of data, and then try to restore to a 256GB SSD. That's a NO GO), you're fine. I do it all the time with the 75+ macs I circulate at my office. No problem. It can be a really slow process, though due to the limitations of your time capsule, your network/network capabilities of the mac, and the SSD limitations (sometimes with the 3Mbps 2011 Macbook Airs SSDs, it can go overnight).
2. OWC's products are great, and carry a 3-5 year warranty (provided you buy the drive from them or a licensed distributor. If you buy on ebay from an individual, you're on your own). I have plenty of both their macbook air and macbook pro retina SSD replacements. They're quality drives. Buy the shells with your first drive (for whatever model). They are extremely handy.
3. You DO have an alternative as of last month... Jetdrive from Transcend. According to their data (which yes, can be skewed), their model out-performs the OWC Aura Pro 6G SSD's. The BEST PART - which is why I'm buying one - is that there is also a much larger drive option: 960GB!! Woohoo! Regardless of size, you'd need their JetDrive 720 model (240/480/960GB option). http://www.transcend-info.com/Apple/jetd...
4. Lastly, as Dan mentioned, there are ways to make sure you're not at risk of losing anything before you use the restore feature. First, with what you're doing, both OWC and Transcend sell the replacement drive KIT as Dan mentioned (which includes an external shell for your OLD APPLE SSD). You COULD (and this method is faster), pull the old SSD (which by the way -- BE SURE TO UNPLUG THE BATTERY BEFORE DOING ANYTHING UNDER THE HOOD OF THE RETINAS!!), pop in the new drive (be it the Jetdrive or OWC version), pop the old SSD into the shell and plug it in to the USB, and then BOOT with one the following methods:
[Assuming you backed up your drive here... either with something like Carbon Copy to another drive, or to an external Time Capsule, etc.]
a. holding option key + r. This will force the macbook pro to contact Apple's network to restore (because the new drive won't have anything on it and that is the default response to a blank drive (using a network connection). You'd then format the new drive, and then reinstall OS X Mavericks (or Mountain Lion -- can't remember which is the default OS X for A1425 model). Then, once OS X is installed, when it asks to restore you info... select from another drive (and then choose your external shell old SSD) and it will restore everything you need (Apps, Docs, Users, Network Settings, etc). The only catch here is that the OS versions are the same. OS X mavericks on the old drive? You'll need the new one to have OS X Mavericks before you can restore EVERYTHING (it will limit you if you restore to a Mountain Lion OS from a Mavericks drive).
b. hold option key. This will bring up the boot menu. Boot from the old drive (external USB3). Then, go into migration assistant and use that to move everything to the new drive (which is now internal). This is also where you could use cabon copy, or the like, and clone your old drive (which you booted from) to your new drive. The problem with CC used in this fashion is that for one... ur running the OS from the drive you want to copy and that will slow it down, and two... it MAY not copy the "Restore HD" drive (the invisible but bootable backup drive installed by OS X on fresh installs).
There are other ways... and if you want to know THEM ALL, msg me. LOL.
****SIDENOTE: My preferred method for this is to actually format an SDHD disk or a USB3 flash plugin drive, and burn a copy of the OS X Mavericks 9.3 installer (using either the actual terminal code which I can give you, and really isn't that bad), or using a software like Diskmaker X (http://liondiskmaker.com/). Then, I boot to the SDHD or USB drive and install OS X to the new mac or new drive, followed by restoring from an external thunderbolt'd drive. I've timed all the methods, and this seems to be the fastest method while maintaining the stability of the data restored.