"What will be the 3 TB drive size? 2.5 or 3.5?"に関する回答There is not enough space for a 3.5" hard drive, so it must be a 2.5" model. these drives have not arrived the customer market yet, but are available for manufactors since a few weeks
"Upgrading ram (is mac ram in any way better than normal ram)?"に関する回答@Josse It would be great, if you would pay the 60-70$ extra fee for the name "Apple" - that would make a small sense - but you didn't even that. In my Mini was "Hynix" branded RAM installed and i replaced it with RAM from Samsung (harrharr, take this, apple!). In other (older) Minis i've found RAM from Transcend or Crucial. Apple bought what they can get for low prices. An 70$ extra fee for less than 5 mins of work (not mentioned that apple don't have to pay 30$ for 2x4GB of RAM) i would only pay, if i knew that the money is directly given to the workers in Taiwan who build my Mac Mini. ;o) @Nejk Since Apple uses the Intel x86-Plattform for their Macs, you can install every "PC related" RAM modules. You only have to look at the specs. For the model "late 2012" you should only use DDR3-1600 (aka PC 12800), because the processor is able to handle RAM at that speed. With older DDR3-1333 (or less) modules you will get a significant lower performance.
"Is there a guide for buying compatible memory upgrade?"に関する回答@Mike, i've heard of some people with five thumbs on every hand and they screwed up the memory upgrade on a mac mini - but if you have a healthy hand-eye-coordination and hande your mini with the needed care, your waranty is not in danger There is not even a tool needed. Just open your mini and change the RAM. It doesn't take a single minute. the RAM modules apple is using are the same modules you can buy at amazon or any other dealer - rember, it's all the same intel platform and the memory controller is embedded into the i5/i7 processor - thats why every DDR3 RAM will perfectly work in your mac mini there are no faster (lower latency) DDR3-1600 modules available as you can buy on free market, not even for apple so do you a favor: save up to 230$ and upgrade the RAM yourself use the money to buy your mini with a fusion drive - this can also be done by yourself (a singe 128GB SSD costs not more than 100$ - instead of 250$ if you buy a fusion drive) but the upgrade and hard disk preparation is quite more...
"Intel HD Graphics Card Upgradability?"に関する回答The Intel HD4000 isn't soldered onto the logic board. ;-) It's an embedded part of the sandy bridge chipset. But that changes nothing about the non existing upgradeablity. On the other hand - the HD4000 is a quite potent graphics solution. Some tests shows that even crysis will run on appropriate framerates. I do personally play games like torchlight, diablo 3 and world of warcraft and these will run very smoothly without raising the system fan to the limits. Absolutely no comparison to the older HD3000 in my MBA.