I will be building my first Myth system later this month after all the parts arrive. I just picked up a pair of Kworld tuners, so now I will end up with four tuners available to me (HVR-1250 x2, Kworld 115 x2).

If possible, I plan to use Myth for all TVs and PCs in our house. I can use MythTV Player on Windows, but I'll need cheap front ends for the TVs.

Can one PC acting as a combined backend/frontend handle recording four HD signals at once while watching a recording? Or, would it be better to build a second PC as a slave backend to deal with the other tuners? Can a slave backend also act as a frontend at the same time? I am considering the round-robin tuner setup described in the MythTV HOWTO. (http://www.mythtv.org/docs/mythtv-HOWTO-23.html#advanced_backend_config)

Depends on the PC you have. I did it without problems using an old AMD Athlon64 3000+ socket 754. Best to have all the tuners in one box IMO.

Processor wise, shouldn't be a problem. You might run into disk speed problems depending on your hardware. I have 4 tuners in one machine and 3 in another, but the most I've ever used at one time is three. And yes, slave backends can be frontends. I have 2 slaves and 1 master backend, and they are all frontends (in addition to a couple of other frontends). Distributed setup is more to maintain, but works for me...

I have 4 tuners in one machine and 3 in another, but the most I've ever used at one time is three.

A big issue to be aware of is heat- I put a PVR150 in with the the Kworld 115 in the other thread, and both tuner card's shielded silver tuner component were almost burning to the touch, until I added a fan to blow over them. I also moved one card so there was an empty slot between them for airflow.