I just spoke to an authorised reseller who said that he can guarantee that only the ram is upgradable and will not void the warranty. A hard drive upgrade will void the warranty.
This is getting ridiculous, surely they should all know the right answer.
Who is 'they', Apple, an Authorized reseller? any one with an opinion?
If you are concerned pay the extra money and have Apple upgrade your machine. This is a very simple issue.
The Short and Simple Answer is Replace what you want, I mean Whatever you want, then Save those pieces that you changed. If you need service from Apple under your warranty REPLACE the parts you changed to make the system look like it is AS SHIPPED FROM FACTORY.
As long as you don't damage anything while doing the Switcheroos you'll be fine.
But in the end if this your first Mac I suggest you just stay with Windows as the Win notebooks made by many companies use the Exact same parts as the Mac and most of the time will be better, Faster, have a longer/better warranty, Include more for a lower price tag. And it will be running a operating system you are use to and have software for.
Honestly there is Nothing Special about a Mac computer. It uses the same exact hardware. The only thing that is special, in any way, is the case it comes in and the cost of it.
If you took that same $1799.00+tax Plus Applecare warranty, which you'll need as to fix any Mac out of warranty is very expensive, $349.00, Plus the RAM and SSD upgrade, $40.00 + $200.00+/- for a grand total of around $2400.00 you can get One Heck of a Windows PC Notebook with better parts, Faster/More RAM and even maybe an SSD of the size you want/Need, and a Much Better Warranty. And you may not need to spend that much for it.
Add in whatever software you will Need to buy for the Mac that you won't for a PC you will be Wasy Ahead of the Game.
Good Luck & Best Wishes.