OK start getting serious rather than daydreaming
you first of all need to set down your business idea and think about how you are gong to make that work (Business model ie how is it going to make money)
You need to understand your target market (and don't just say everyone that is pathetic - properly think through who will use the item/service, who will buy it and who will benefit from it) If you struggle with being more specific think about it in reverse - who has money, how can I tailor my idea to their needs and market to them, and go from there. Be prepared to review this every few months to ask is it working, is something else working etc
Start NOW, get some pen and paper and start planning things out, Local Enterprise groups - networking groups, chamber of commerce, small business network and so on - get on them and go to a few sessions get a feel for who is there are they target market or can you learn from them
Enterprise Nation is a good website and there are plenty of others around that can help you get contacts, get mindset and locate people to help with funding.
You will not need to cover your "salary" as such - think about what you spend on and what you will need if self employed e.g. cars, shoes, travel, clothes for work what will you need compared to now even things like if you currently buy your lunch every day - you will be eating at home. Earnings are likely to be low so tax and NI become less of an issue. PLAN PLAN PLAN then DO IT