How to handle payment processing for a new self-employed business?

[Gary-1]

I’m in the process of building a site and had hoped to make the site live on the 6th of April. My background is as a sole trader for thirty-five years working as a photographer. I retired from photography five years ago, moved to an island in Orkney and have spent the last five years renovating a property. I have the personal information required for setting up shopify payments but no business information apart from my UTR from previous self employment. I’m reading lots of horror stories on the forum about blocked payments and payments being returned to customers.

My website, selling antiques and vintage items, will be a part of my self employed income. I haven’t had to put in a tax return for the last 4 years and when I do register with HMRC again because my self employed income will come from more than one source I planned to register with HMRC in my own name, not the name of my shopify site.  

I can’t see how I can register with shopify payments or any other payment processor without business details but as I’ll be newly self employed from the 6th of April after taking five years off I don’t currently have any business details, unless I’m missing the obvious this seems like a catch 22?

Hmrc allow new sole traders to register within six months, do I need to ignore that and immediately register a business in the name of my shopify website on the 6th of April and avoid making my site live until I receive something back from HMRC? 

If the above means I don’t qualify to set up shopify payments could someone suggest an alternative payment processor for the UK. I’d be interested to hear other peoples experience of launching a new site but not yet being registered with HMRC? 

Sorry for the long post, thank you in advance to anyone who offers suggestions or advice.