Hi,
I've just written an online admissions portal for this exact purpose. SIMS has an XML import routine for applications. I suggest you use it, as it does a lot of things under the hood as applicants and their contacts need checking for duplicates (all of which it handles). It's aimed at the Independent market, but it will work with SIMS for normal state schools (we are) and you can get a licence for it.
https://www.capita-independent.co.uk/products/sims-registration-admissions-independent-schools/import-applications-and-enquiries
Our portal goes a little further, by providing live tracking of applications - the applicant can login and see where they are in the process, as well as sending automated emails, etc. This uses a .net Web API I wrote, which sits on top of the SIMS Business Objects. May seem like overkill, but we use it for other purposes than this. You could use the CommandReporter tool if you need to extract data in a similar fashion. Feel free to PM me, if you want any advice.