How to get started?

We have never had any real need to run informix, all our databases are managed by our own in-house systems and very rarely require any user input (data flies in from remote sites, processed and pushed out again). However, we now find ourselves in a situation where a group decision has been made to devlop all new `group' databases using informix. The other companies in the group operate on a variety of platforms, the parent company operate a small number of SCO based informix PC's. As this is all fairly new to us, what do we need to get started? We need to be able to build GUI (X/Openwindows/Motif) and forms (ascii terminal based in the main) interfaces, access databases from our own software (written in C and C++) and work over a network (between sites). We run Sun systems at 4.1.2 and above. Any clues would be welcome before I start talking to suited informix sales people :-) The 'technical briefs' I have through so far seem full of a variety of options and lots of large numbers.