If you are a good healer, you should have no problems healing. Oe you hit 50's or so, be on the lookout for two sets of gear, one for damagingsoloing (+dmg, +shadow damage, mana5, intellt) and a separate one for healing (+healing, spirit, mana5, intellt). Being a fairly good healer (2 years perfting healing as shadow :P) with dent but not great gear, Ian main heal most endgame 5-mans with minimal support, espially with a good group (high dps andor lots ofC). Healing as shadow will not be even possible in heros, and probably not main-healing Karazhan or raid; HOWEVER by that level people know how good shadow priests are and you shouldn't have mh problem getting into heros as a shadow priest. I'd take Shadoweave Tailoring definitely, espially if you get to the point where youhoose and you know you want to stay shadow.
1) I healed through Sunken Temple as shadow. BRD is the real stking point, though it might be easier if you have -60s (haven't been there sie theaphange). I also healed some of the early instaes (Ramparts, Furne, Slave Pens), but it got progressively harder to heal the later ones. Youan do it, just any mistakes by the tank, and you'll have a hard time rovering. An off-healer would almostertainly be nessary for some of the bosses unless your tank is godly. The final bosses of Aatraz and Halls would be... interesting with a shadow priest main healer with no support. 2) People will be pissed, bause the two stking points on any party are healers and tanks. Just point out that they're not a healer either. Shadow is a great sp, I'm always happy to have a shadow priest along. 3) Shadowweave if you're shadow, primal mooloth if you're healing. Its really just that simple. The tailoring eps are at, or surpass, the level of tier 5. They areertainly far beyond tier 4. There's just no reason to pass them up.