Hi Kieran
Good luck with your venture. I do not know what market you are in or who your customer base is but you should be able to compile fairly standard terms and conditions either by googling examples of T's and C's or by 'seeking inspiration' from those of competitors / similar businesses.
Unless you know your customers well - I would not give credit automatically. You should continue to promote 'payment on delivery' as your standard terms with an option to apply for credit facilities for corporate clients. If you are going to extend credit to several customers - be sure you factor in the cost of this to your pricing model. You will need to devote time (either your own or someone elses) into vetting credit applications, controlling these credit accounts (including credit limits) and ultimately providing for some level of bad debt.
Personally - if you feel you must offer creditI would suggest that you take your existing pricing, increase it by about 6% and then offer 5% discount to customers who pay in advance !
Best of luck with this
Dicey