ERP Systems are notoriously difficult to implement without huge costs, typically run over budget and time. I have worked in software development and been on implementations that were quite disasterous.
That said, we (I was one of the tech leads) recently implemented a sytem in 11 months that covered all of ERP, CRM and Service Management and totally replaced our previous system. It was done on time and under budget. My company is about 1200 employees and we employed 50 full and part time employees on the implementation. We support the system in 3 manufacturing centers and 7 countries with a team of 10 developers and 4 business analysts. We manufacture and ship international, run paperless warehouses, interface with carriers, do electronic banking. We use electronic trade, automatically prepare customs documents, drop ship anywhere in the world and take orders up to 7:00 PM at night and still guarantee same day shippimg. We could not run the business without extremely sophisticated ERP.
Whatever you do, talk and go visit other companies who have implemented the same software as you are considering. Ask them what went well and what went wrong. Find out what they'd do differently today. Any software vendor will give you a list of reference accounts and most companies will be willing share their experiences.
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