Building a computer from the ground up only takes an hour or so but loading the operating system, then all the Microsoft updates for it, followed by all the usual useful software (like Adobe Reader, etc) and configuring the Internet connection, loading and updating an anti-virus programme etc. usually takes another 3 - 4 hours.
Windows 10 is now Microsoft's latest operating system. The jury is still out on this latest offering although most agree it's vastly better than the previous Winows 8 or 8.1 - and it needed to be. It has the "flat" impersonal look of an apps based OS although old favourites like the "Desktop" are back by popular demand. Some will miss the nice familiar "eye candy" we had with Windows 7 although Windows 10 will open the door to third party apps being available. This is of course already well established as far as the popular Ubuntu OS is concerned and many may possibly flag Windows 10 completely and opt for Ubuntu in the future.
The tech fraternity is unsure at this stage what will happen from here on as it's understood at the moment this will be Microsoft's last operating system per se and will simply be added to with modules, apps, etc. as required. While it's currently being offered as a free download to users whose systems qualify (through Microsoft Update) this will only be the situation for 12 months. After that, if you haven't upgraded, you will have to purchase it. It's licencing is now exclusively based on the equipment currently inside your computer so it's rego number is tied to that configuration therefore, be aware, making major equipment/configuration changes further down the track could cause possible licencing issues. As for the future it's suspected that Microsoft is intending that eventually we won't own the operating system as in the past but will have to pay an annual subscription instead.
If you elect to install it for free through your Windows Update do a little homework online first as some software and/or peripherals you use now may not be compatible with Windows 10. For instance, Virtual Windows XP, that you could run from within the Windows 7 environment, does not work in Windows 10 so any XP programmes you had been able to use in Windows 7 will now be unavailable. Also Mail in Windows 10 does not support POP3 mail clients - you have to download Windows Live Mail to get POP3 mail working. Unfortunately nobody knows how long Microsoft will continue support Windows Live Mail. We can only hope some third party will come up with a mail app for Windows 10 that will support POP3.
The primary consideration when selecting components is to ensure as much "future proofing" (upgradability) as possible for a given budget. This also depends on what you want to use the computer for. If it's just Internet surfing, email and some word processing (ie: letters, business documents etc.) then you don't need a superduper machine but it still needs to be fast enough to cope with present and future programmes.
If you are into "gaming", offline or online, then you do need a machine with "grunt" - particularly in the CPU (Central Processing Unit), RAM and Graphics areas. These don't come cheap of course but can be immensely satisfying - especially when the computer "waits" for you rather than the other way around.
If you are considering having a purpose built computer talk to me first.