Hi. In the US, there's a group called SCORE (part of the SBA). There are 10,000 of us nationwide that help mentor small business owners - for free at hundreds of locations. Check out https://www.score.org. Not sure if there's something similar in the UK...
connect with me, I can mentor/coach you through it. www.raddstudio.com
Absolutely! See my website and credentials at www.atmgrants.com
The first thing I would say is to set aside any plan for funding applications right now. You need to concentrate on your business plan, testing your assumptions, validating your product/market fit, and building a marketing plan. Those research steps will determine both whether the idea is something that has a chance of succeeding (after revisions) and how much in resources it will take to execute. Without this in-hand first, you will not succeed in obtaining funding.
So, to get support in building your plan, I recommend starting with one of the templates from SCORE (mentioned by someone else). https://www.score.org/resource/business-plan-template-startup-business Although SCORE is not in Scotland, there are probably other similar organizations in the UK that you may be able to find through your local minister's office or chamber of commerce. Call and ask what the government has to support entrepreneurship and small business. I'm sure there are various programs to access. Start with someone who can review your plan as you've written it using the template provided, and coach you through revisions that are needed.
While that's going on, there's nothing stopping you from writing a list of assumptions you've made about your product/service and audience, then testing each one of those assumptions individually. You can also spend time validating the idea you have is something people actually want, would spend money on, and find out where you stand competitively with other solutions (that may be indirectly competing).
Those are reasonable starting steps. Come back and tell us what you discover.