You still really need to have an RS232 interface as that is the only way you can install / configure your C-Bus network using the C-Bus Toolkit. Actually there are some other ways - via Touchscreens, Ethernet or the PAC controller but most people use the RS232 - ( BTW - if you're interested in a reduced cost RS232 unit get in touch via PM as I have a brand new one spare).
Re scheduling events - there are a number of applications around that can schedule xAP events - including the free "xAP Floorplan" from
http://www.mi4.biz . However I must say that I would tend towards making your C-Bus lighting install as standalone & robust as possible and hence trying to reduce any dependence on a PC to minimal. PC's do crash as I'm sure you know. Adding the extra smarts using a software application is the route I took, but the core C-Bus system is independently functional. To an extent scheduled events may not be critical - but a switch turning a light On or Off is. HomeSeer can also act as a scheduler, every group (light) on C-Bus becomes a HomeSeer device and you can trigger based on it changing state or you can script/schedule changes , even using logic as needed.
xAP is simply a protocol - perhaps a reasonable analogy is TCP/IP - it is the 'language' mechanism by which other applications communicate eg web browsers, email, this forum etc. Really you don't need to know anything about TCP/IP to use a web browser and xAP occupies that same ideal. Unfortunately as xAP is new and still finding it's feet it doesn't enjoy that transparency and you have to work a bit harder to get it all talking.
I am just an enthusiast who designed the gateway for my own needs - when others had the same needs I had some boards professionally manufactured - it's still a 'hobby' project though, constantly evolving ( read never finished !) and I only make the boards up in small numbers, so sometimes people have to wait for the next batch...
K