Unfortunately MediaPortal doesn't support extenders at the moment, so your only choice with MP is to build your own client pc, the benefit with this of course is that you get to decide exactly what components go in it and it's perfectly possible to build a silent pc that is up to the job.
With the DVD rips you can also store them in their native VOB format and MediaPortal will play them just fine, no need to mess with automounting and what not, obviously some people prefer ISOs and ultimately it comes down to a matter of preference. Either way, you can have the full DVD experience.
As for physical Blu-Ray discs, at the moment MP doesn't natively support playing them (which you'll find is the same with all media center software due to lack of support in windows itself), however you can use
this plugin which will start PowerDVD and play them for you.
I've only had a play around with ripping Blu-Ray's and had some stuttering problems playing over the network and even off the local disk, which I'm sure was to do with codecs but I've never really spent too much time looking into it.
I'm not sure whether you'll be able to get the full Blu-Ray experience with ripping, probably not via mediaportal itself but as with physical discs you may be able to use PowerDVD, personally I've never been bothered with all the menus and extras on my DVD rips as I can always put the disc in if I need to.