From the offset (haven't even read the entire thing)
Tip 1: If you'd like to have cost increase and sit with an inflexible system that doesn't suit your company needs, then buy off-the-shelf products.
Personally, it has cost a company 15x the amount of money it would have cost them writing their system from the ground up with the features they need.
The reason off the shelf products LOOK good is because the development cost is spread accross alot of people, but it's generic and usually can't do what you want. "It can have custom addons written for it" <-- Sweet... I'm at a company who lost 250 million Rand because of this.
People think cutting cost by buying off the shelf products will save them this huge amount of money, when in the long term it costs them more to do what they need the package to do and make it do it that way (or walk into several "brick walls" with the software they have, unable to do what they want) than it would the minimal cost saving it saves them now....
Sure, for some it might work, but any business set on growing in the future needs to think long and hard before running their website off of Joomla! and downloading/installing a free e-commerce package to handle their sales. Sure, it might be adequate now, but 3 years from now it will cost you more just to change systems...
Financial systems you CANNOT cut short. If you don't have the cash to do it properly then don't even think of starting...