Applicants who would like to apply for innovator visa must provide a business plan which will be endorsed by an authorised organisation which is specified by the UK government. The main condition for this visa category is that you must invest £50,000 for each innovator applicant. If you have a co-innovator or a person who will be a partner for the business must invest £50,000 in the business to be able to be granted the visa. On top of these requirements, an authorised organisation must endorse your business plan. Only after that, the main requirements will be met. There is also English language requirement which is CEFR level B2 and also you must prove that you have enough funds to cover yours costs while in the UK. This money cannot be the money you are investing in the business.
Start-up visa, on the contrary of Innovator visa, does not require you to invest in the business. You can get investment from one of the endorsing bodies. Before you apply for this visa, you must have hold minimum of £945 in your personal bank account for 90 consecutive days. This is asked to prove that you can cover your costs of your travel to the UK. Start-up visa is originally created especially to attract more international talents who are able to create start-ups in IT sector. There is no sector restriction on this visa category however, most of the encoring bodies are from technology sector.