I plan to build a desktop program that able to publish/post my property listing in all free classifieds web site (my country only, 30 targeted site).
What i have to do is key in all detail, upload photo, then submit, it will automatically submit all post other (targeted and register) website.
First site Submit:
1. My own site (wordpress base with custom theme).
then follow up by other 30 public site.

What i going to do with this script.
1.Use for my own property listing. (thanks to my property site, i m a part time Property Agent now )
2. Sell to other Property Agent (subscription with very low monthly subscription fees, my aim is their property listing, not software income).

I need a idea should i use online script or desktop ?
cause i have huge Property Agent (currently 400 agent and increasing) that currently with me and all of them wanted to use this script for their own listing, that make me worry i need strong server and bandwidth to handle it ......

If desktop, i will be worry on software/OS compatible issue ....
please input