Depending on the amount you can financially put up at the beginning will determine whether you start off very small or quite large. This depends upon the nature of the business you intend to start. Can you set up the business and work from home or are you going to need premises and lots of equipment and how many members of staff will you need to take on. Its no good getting the equipment and then finding out you cant afford to take on the neccessary staff to run the business. The more capital you can put in the more options you have.
The nature and complexity of your business is another important factor. Are you planning on starting up a business that will have plenty of competitors to battle against, such as a mobile phone shop or a clothes shop or will your business be something that may not have many competitors but if no one is interested in your product you are not going to make much of a profit.Without doubt budgeting should be considered in all aspects when it comes to planning your business and the size of it and it is important to be realistic about it. Better to start off small and grow then to overstretch yourself and struggle.