where's the Moon Rune?  Never found that one. 

Just make sure you have 30+ on health and 25+ on the weapon skill of choice, Otherwise you'll have a really hard time because chalice dungeon enemies hit hard, and can take a lot of hits. Level 4 chalice enemies take between 700~1500 depending on enemy, and Level 5 chalice enemies take 1000~2500 to bring down. You'll need the stamina depending on the weapon. 6~7 R1 hits per bar is a confortable number I've found, anything below that, and you'll be having problems running out of stamina.

Ah, Bloodborne rant time, YES!!

I totally got stuck at one point after unlocking two additional tomb stone things(to give an image of progression). So much so that I read the Eurogamer walkthrough carefully to not read spoilers just to where I see something I missed. To my great annoyance, I missed (and I felt that there should me more to the area), the stairs to the right in Old Yarnham, where you go down to the area where the guy shoots you with the minigun.... somehow.
BUT, as someone mentioned, that is optional and doesn't open up a path of progression. So eventually I concluded that I missed something else. To my even greater annoyance, I discovered reading further the walkthrough that there is a ladder in the freekin library place!! How in the world I missed that I won't know.
It's frustrating because I clearly remember that in both places where I missed these obvious things I felt that there should be more and LOOKED!! ... TWICE!!
It's more depressing than frustrating. Now I fear that after I kill the thing in the lake, the game will not open up again, because I must have missed something else somewhere... again.

The same thing happened to me in DS2. I think (hope) it's because I don't play often, and when I do my style is slow and careful, so it takes me a long time to go anywhere, hence I forget what is where and things.

Or I'm just getting old.

Don't worry, the game will put you on the path to progression after the lake.

Think I'm playing about the same as you (slow and careful - haven't felt this nervous or tense during a game in forever), and have certainly missed at least one optional path I know of thus far.

Good. Now if I could only figure out an evade pattern from the meteorite things other than "panicked roling to the right" (well, not that panicked, but certainly either lucky or unlucky). Last night nobody answered my bell.

There are a few things you can do to make that boss easier to deal with. First, always kill the adds before the boss. This is easier done if you are relatively close to the boss, as he then does a ground AoE that's arguably easier to avoid than the meteors. Also, in case you didn't notice that all these monsters have a rock-like head, hit the body. Avoiding the meteors (which will have to happen at least once as you approach it) requires a bunch of dodges in a row, sometimes you can avoid them by just running; regardless, you may want to consider boosting your Arcane defense if tha5 attack is causing you the most problems (equip the Arcane Lake rune, the Student Outfit & Pants).

Thank's for the advice, but I defeted it last night using another tactic.

Indeed, if one stays close, it will use AoE attacks, which are much easier to avoid. But instead of attacking the helpers, which I fould was frustrating because eventually I would get meteorred, I just ran around from left to right, trying to flank the thing and get in one perhaps two hits then roling away to dodge the helper attacks and then runnign a litle more to escape the AoE. I had a fire weapon, but the sides of the things are vulnerable, so I presune a normal attack weapon would have worked too. A fast one that gets two quick hits in and leaves enough for a rol or two seams to work well.

read about that too but then if you attack his friends in old yhanam he'll shoot you again lol.

Ended up learning how to sprint (derp) and killing him. 

Then i died to the blood starved beast in a scary boss match lol.