Vallery - loans and lease agreements definately factor in affordability, so yes your income would come in to play. If your a new start up, a good business plan will come in useful.
Before starting an agreement, you should consider the differences between loans and leasing:
With leasing your not BUYING the goods, so the monthly payment goes against your profit in the same way as when you buy chemicals, training courses etc (ie it is a liability) at the end of the term the goods go back, OR you pay a nominal amount (maybe as little as £100 - called a 'peppercorn' payment) and keep the goods indefinately. Because you are not incurring interest there is no APR, but the expensive part is the admin/management charges levied by the leasing company.
When you take a product on Hire Purchase you are buying, so you can claim tax relief on the interest part of the agreement (and possibly depreciation). At the end of the term, your payments end and you own the goods.
Lease payments will generally work out more expensive on a monthly basis, but they are more tax efficient.
Good luck all
Ash