Advice on where to begin with product integration

Hello! I'm sorry if this is the wrong place to post this question - I couldn't find an all inclusive extension forum.

Here's my question, I have Data Assist, eCart 5, Security Assist, the Power CMS PHP code, Universal email, Validation Toolkit etc... I need to build a very custom ecommerce store. I've also downloaded the eCommerce recipes.

I'm having a chicken and egg problem here. I want to build my store (with no payment gateway) I need an admin backend to manage store products and look at orders, I also need to set up this store as a secure site that needs a password for access to the entire store (including catalog pages), I also need to create the shopping cart and the product catalog. I need my shopping cart to store the orders in a searchable database that is also accessible via an admin panel. I'm familiar with setting up dynamic sites and database integration with Dreamweaver and basic PHP integration and advanced CSS. I've worked with eCart and DataAssist and most of the other extensions before.

That being said - I was wondering where to start? Do I build the catalog/store first then the admin backend? Or do I start with the log-in and log-in admin for this site? Or do you suggest that I build the admin first before the store? If there is some Getting started guide that leads someone through this process, please point me there - I couldn't seem to find it.

My second question - is it possible to just adapt the Blue Sky store's code in the Solution recipes? I know how to point one of those sites to my databases and reskin it. And will that easily integrate with the Power CMS code?

I'm just wondering if anyone could recommend the best approach to your product integration here. (I couldn't use PowerStore or any other pre-built store because there's a high degree of customization needed in my store.)

Many thanks for your suggestions and feedback.

Carlene