Where to start creating an online store?

start by finding the audience — if there is a buyer, especially a permanent or constantly arriving, the rest of the details.
try first to do just the window (even static), with a telephone order and/or order through the feedback form.
when you have a flood of orders for which the address book is not enough, then there will be money for e-shop (at least you will be able to devote to the design and creation of sufficient funds).

1) it all depends on what You expect. If the plans are serious, it is better of course slopes and keep a staff of programmers to zapilivanija functionality (and it will very often)
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2) XS
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3) no, you can pay it is not necessary. If you're selling a product will break through the checks offline. Just on the website lay out the details of the company (legal address, INN, KPP, Bank account, etc.)

In General, it all depends on how complex you plan to store, and what goods will sell.
In General cases, I recommend as a CMS — Simpla (http://simplacms.ru).
Very simple, convenient and available in the development control system – both from the user's point of view and from the point of view of developers.
The design depends on the requirements, it is difficult to say, in an average kachestvennyi design freelancers charge around 10 thousand (4500 rubles for the main, plus all necessary internal).
But in the case of using Simpla – even with basic knowledge of HTML and CSS from standard templates (set 2 PCs) dopilivat what you want.
If you need help, please contact us.

For the day, Asil shop using joomla+virtuemart even with zero knowledge.
There are many forums on these issues and of course, there are video tutorials.
z.s. the PM can give a couple of links if interested.

1) in-House engines well, but you need to keep a team of programmers, and to write functional web store a few hours will not work. But, as said previous person — depends on your needs.
We are now set to move shop just on the finished engine. Chose Magento, but do not know how much was the right choice, because from scratch it quite difficult to understand. But programmers familiar with this pull on design is not very complicated.
OSCommerce is better not to look — the old system, the code is written badly, quite a lot of bugs can come out.
On Habre it is possible to look for a review of ready-made solutions.\\
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2) prices — from zero, if to take ready-made skins and ready to pull the engine, to the "how much."

Don't know what functions you need in the store, but OpenCart as a variant of the simple shop, the benefits of MVC, open source, has all the necessary modules

About CMS, in my opinion, the best option is Drupal + ubercart module