Hi Jim, nothing wrong with having ambition, without it we'd still be in the stone age! Can't give you any specific advice but maybe some general...
What is the county competition - how many shops are there in your county. Check out those (in a neighbouring county so as not to make them think you will be in competition) who have a similar economic/populace base to the area you plan to set up your shop. If they're struggling, find out why and whether you can overcome their problems.
What is the local competition - too many shops already will mean meagre pickings unless you're going into a niche market or undercutting everyone else.
How big is your customer base - setting up a shop in a sparsely populated area means few customers and meagre pickings.
Where to have your shop - how many potential customers pass your shop frontage - on foot, car, bus, etc. If people can't easily see the shop then you will need to invest more in advertising.
How accessible is your shop - you will need ample customer parking in front/behind as cusomer won't be interested in buying from you if they have to carry boxes to their cars a long distance. Also your suppliers will need good access.
What are your combined overheads - you need to know what your overhead monthly outgoings (business rates, rent, paye, insurance, electric, etc) are to enable you to determine the minimum sales you must make to break even. This will determine how likely the business will succeed.
Advertising - This will depend on the factors above but you will have to get out and about to sell yourself.
Internet trading - Consider setting up an internet
tile shop as well, to boost your shop income.
Staffing. You need to have people who know the
tile business or are prepared to learn it fast. It's no good having someone who can't/isn't prepared to learn as you will quickly loose custom.
Tilers - This is the right place to find tilers!
Hope this is of some use...