What type of computer should I get 2015?

I need help finding a computer here are my requirements:
-NOT a chrome book
-under 675$
-capable of playing games like minecraft and sims
-good for a high school student
-laptop
-easy to carry around in a back pack

Minecraft game mode changing problems?

Ok, so me and my friend play minecraft on realms and the thing where you type "gamemode c " or s in the talk bar then it changes the mode to survival or creative. Well some reason it doesn't allow me to do that. It just says in red, "you are not permitted to use this command" me or my friend don't know how to change that so could you help please if you know what I'm talking about?

What am I doing wrong on my YouTube gaming channel?

I have been on YouTube properly for about 4 months now and in that time I have learned a lot of new ways to edit and increase the quality of my videos. However, in this time I have gained very few subs (26 subs at this moment in time) and a mixed result of views on each of my videos. I appreciate all the people who have subbed to me and I try to respond to their comments either on the video or on one of their videos, but I'm looking around on other people's gaming YouTube channels and some have like over 200 subs due to 7 videos (that were the same quality than mine) within a month of being on YouTube. This has just led me to believe that I must be doing something wrong with my channel but I don't know what. I share my videos on social media like Facebook and twitter and I post my Minecraft videos on a forum.

Here's a link to my YouTube channel so you can take a look
https://www.youtube.com/...Fv7AQ/feed

Is it possible to have 2 MC accounts on one computer?

Is it possible to have 2 MC accounts (which are completely separate) on one computer? I have 2 user accounts on my computer, 1 for my brother and 1 for me. I want to be able to play on my own minecraft account, so I don't have to use his. Is that possible? Or is it possible to make 2 mc accounts on 1 user account on my computer, in a safe and not too difficult way?

Every time I try to run minecraft, I get a crash message error I don't understand?

I can't get minecraft to work, and it says a bunch of stuff about Java I don't have a clue about. Here's the error message: [09:04:44] [Client thread/INFO]: Setting user: gvbucksnort7
[09:04:44] [Client thread/INFO]: (Session ID is token: e2ddfe89cf38423cbf43e73414238123:7…
[09:04:48] [Client thread/INFO]: LWJGL Version: 2.9.4
[09:04:50] [Client thread/INFO]: Reloading ResourceManager: Default
[09:04:52] [Sound Library Loader/INFO]: Starting up SoundSystem…
[09:04:52] [Thread-6/INFO]: Initializing LWJGL OpenAL
[09:04:52] [Thread-6/INFO]: (The LWJGL binding of OpenAL. For more information, see http://www.lwjgl.org)
[09:04:54] [Thread-6/INFO]: OpenAL initialized.
[09:04:54] [Sound Library Loader/INFO]: Sound engine started
[09:05:15] [Client thread/INFO]: Created: 512x512 textures-atlas
#
# A fatal error has been detected by the Java Runtime Environment:
#
# EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x277a3e88, pid=3752, tid=2100
#
# JRE version: Java(TM) SE Runtime Environment (8.0_25-b18) (build 1.8.0_25-b18)
# Java VM: Java HotSpot(TM) Client VM (25.25-b02 mixed mode windows-x86 )
# Problematic frame:
# C [ig4dev32.dll+0x3e88]
#
# Failed to write core dump. Minidumps are not enabled by default on client versions of Windows
#
# An error report file with more information is saved as:
# C:\Users\GAV\AppData\Roaming\.minecraft\…
#

# The crash happened outside the Java Virtual Machine in native code.

Quicktime Player is very laggy?

I have been using quicktime player as my recorder for minecraft and i have noticed that when i check the recordings they are very laggy, i have tried changing settings for minecraft such as max framerate and render distance but it is still lagging. Is there anything i can upgrade on my macbook pro os x yosemite to solve this problem? My mac has 4GB of memory if this is important