You cannot empower power on any cleric buff, which means that basically no empowerement is needed on buffs (SP consumption and cooldown is blah as you use them once an hour or so, duration adds next to nothing : 5 points in protect duration adds 3 seconds, wow that's great for a skill that lasts 1 hour !)
Your best friend for cleric skills questions :
http://www.fiestafan.com/wiki/Cleric_SkillsSidenote on solo clerics.
Solo clerics either add all their free points to STR or use the 25 SPR / STR build (but due to our low damage, the best build would be full STR) and empower at least bash CD and power. Bleed and trip are debatable, they're not extremely useful at the moment but it could change if a secondary effect is added to them.
Most solo clerics will prefer maces because as we cannot spam skills (unlike fighters) the attack speed of the weapon actually matters. I won't try to find that again but someone, on Outspark's forums, compared the damage over time of maces and hammers and maces dealt a lot more damage on strong enemies (which is what you'll be fighting most of the time). Besides the CD of bleed is 10 seconds (7s fully empowered) while it's 15 seconds (10.5s fully empowered) for trip... there are also 10 levels of mace mastery compared to 8 levels of hammer mastery... so at the moment I think maces better... would be different if trip added stun
I hope this helps.
(edited to add the weapons mastery)