Five years is a very long time, but it is never too early to start planning, there is some very good advice above, but also consider.
First and foremost everything takes longer than you think and costs more than you think, plan well ahead. Do not look to have your phone line installed the day before you go live for example. In fact try and have EVERTHING in place at least two months before you go live.
Never underestimate the team around you, be they services you pay for, accountants, bank manager, lawyer, solicitor etc or employees. Good ones will make your life much easier bad ones can make your life very unpleasant indeed.
You maybe the best engineer in the world but you will be short of some skills you need, at least at the start you will need to cover all aspects of the business, PR, sales and marketing, book keeping the list goes on and on, learn all you can.
Some things are foolish to try and save money on, many are not. Hunt around for the best place to buy second hand furniture from for example, if time is on your side you can get as new at a fraction of the cost of new and at the end of the day a filing cabinet is just a filing cabinet.
Join your local business group in the UK the chamber of commerce or the federation of small businesses, make contacts, as well as providing a service, you will need services provided to you. Planning ahead will save you money without effecting quality, failing to will probably mean one or both suffer.
Keep a very tight grip on the budget in the early days or at time of expansion, moving office, taking on new staff etc. 75% of new businesses fail inside 6 months in the UK, the biggest single issue is cash flow.
Most importantly of all, enjoy the journey.