Magento e-shop fix issues, optimise from top to bottom, squash bugs

Brief My company is based in Greece, and my e-shop sells hair accessories, cosmetic jewellery and hair extensions. The e-shop is in Greek and English (Greek being the main language but I don't think that it will be a problem at this point) and I sell wholesale and retail. I used to have my company's e-shop on a custom platform. A software house in Greece designed a Magento 1.9.2 e-shop for me and migrated the database accordingly. Apparently, they didn't do a really good job and were very bad in their timelines so I'm looking for someone to have a look at the site top to bottom, optimize it, squash all bugs and fix the things I want to, to basically make it work properly. I also need someone to design and customise the csv necessary to upload my products (simple and configurable). In the previous website, I've had products that were not uploaded properly, so I'm basically doing this from the beginning, with new photos, and inputting all proper information in Greek and English, Wholesale and Retail according to Google's SEO guidelines on metadata etc. The database at the moment has about 5K products (simple and configurable) and most of them don't exist in the retail version, just the wholesale. Imagine that if I’m selling a product like a headband, in wholesale (simple product) I sell it in dozens that have all colours assorted (it might be six different colours x 2 pcs each). In retail though, the same product needs to be sold individually for each colour (configurable) because someone might want one yellow headband and two green out of the six available colours. I am attaching a file with what needs to be done to get an idea.