Help building a new pc

My favorite line of of desktops has been the hp elite small form factor ones which have provided good overall function while not taking up too much space.

This is more than likely going to be a gift for a sibling considering his computer needs an upgrade

I wanted to build something similar to these in terms of size ( of the hp sff elite series) but better function. I did already look at the newer revisions and they are like $500 or more.

I liked the integrated audio in the motherboard for hp computer so i am not sure if there is a motherboard similar that can offer such a feature as well

The size of the casing is probably one of the main things i would care about i definitely would not like anything bigger than the size of the hp sff elite series something a bit smaller i would consider.

The main use for the desktop would be for video editing, medium high multitasking and having lots of programs open , and streaming. I think the integrated graphics will do but if someone can recommend a low cost low profile card for this build id welcome.

I would aim for i newer generation i5 as an i7 probably won't be all too different for what the pc will be used for ( and it will cost more.)

I was hoping i could build something on my own for about $350 or less.

Some things i already have:
Spare atx 400 watt power supply
Memory
Hard drives
Optical Drives
Windows 8.1 operating system

Some things i will need:
Motherboard ( micro atx or mini itx due to slim casing)
Processor ( prefer intel but will do amd depending on recommendations)
Case
Possibly power supply depending on case size
Video card


I wanted to put windows 10 on this new pc for my sibling but i don't know when the non preview release will be out, so meanwhile i was thinking of using linux and then when windows 10 comes out to install that since i think he will like it.

Any suggestions much appreciated, keep in mind i am in the states ( for ordering parts)

 

A small form factor, video editing and lots of programs running will mean compromises. You will want a ton of RAM (12 - 16 GB) and all the CPU you can muster to speed up multiple programs.
some thoughts:
http://pcpartpicker.com/b/yHxYcf
you will need a LOT more CPU for video

 

Opinions on this so far?

MSI-H81I-LGA-1150-Intel-H81-Mini-ITX-Intel-Motherboard

Intel-Core-i5-3570K-3-4-GHz-Quad-Core Processor

Antec ISK 300-150 Black mini itx case

Probably should have gotten an amd combo i saw like a week ago but passed on it because of amd which i wasn't so sure about getting.


https://slickdeals.net/f/7598298-am...-asus-a78m-mobo-bundle-289-99-a-r-w-fs-newegg