I'm not familiar with the rules any more but I'd check with an accountant on how far back you can claim from registration date.
When registering for the first time -
You can reclaim VAT paid on goods or services bought before you registered for VAT if you bought them within: 4 years for goods you still have or goods that were used to make other goods you still have.
So you can claim back VAT on any equipment you've bought in the last four years.
But only 6 months for services
You will need to use a Making Tax Digital system to submit your returns. That costs around £5 a submission, so rather than submit every month, better to do it quarterly. I use EasyMTD VAT. Your first submissi0on is free then £21.59 for 4 tokens and you can reclaim the VAT on that