Can we Customize and Use Both Forms and Self-Service for Budgeting and Forecasting in Oracle Project

 I have a requriment at my  clients end which goes out to build typincal accounting based budgets in Forms in Oracle Projects and Operational part of budgeting, progress, forecast etc to be taken up in the Selfservice(HTML pages) integrating them to a third party service provider. In such a case I wanted to understand the the probable hurdles/bottlenecks one would head into in the long run. Is it that my client has to stick to one the options i.e Forms or Self Service.  I request you to please help me out on this. Our planned customization will not upgrade the budgets