Planning in BI

Hi

We are at BW30B patch 15, EP 5.0 with SP5 and have not implemented SEM. But we want to migrate our excel based sales budget / planning to BW. Our planning model is very close to "manual planning" as depicted in the product literature for BW. We want to develop a custom application which will trap the relevant excel based information and also the documents and later transfer the same to BW. Will it be possible for some one to share their thoughts, guide us to more detailed technical info via links etc

regards

Harsh