Sorry for the long post, but I figure if I'm going to ask for help, I should give as much detail as I can.
I'm fermenting my first lager now. This was one of those $20 anniversary kits from AHS, so I bought the extract kit with grains even though I normally do all grain - figured it'd be a cheap way to try a lager for the first time since the extract kit was priced the same as the others. I used 2 packs of S-23 for this 1.052 OG pilsner (5 1/4 gallon batch). After the boil, I threw away the AHS instructions which had called for pitching warm, then cooling. I cooled the wort to 50º F and while it was cooling I rehydrated the yeast at 72º F, fed it a small amount of wort and cooled it over about a 4 hour period to about 48º F and pitched it. I wasn't sure whether or not to aerate with dry yeast (I've read pro and con) so I gave it about 45 seconds of O2 through a .5 micron stone just before pitching.
I set my Johnson controller for 52º F, so the beer spent most of the time at 50-51º F. Fermentation kicked off within 12 hours and proceeded at a steady pace (about a bubble every 2 seconds from the airlock) for about 5 days, then began to slow to one bubble every 4 seconds. I raised the temp setting by 1ºF - the next day it was one bubble every 6 seconds, so I raised the temp setting another 1ºF to 54º F. Later that same day (eighth day after pitching) I decided it was time to check if it was time for the diacetyl rest, so I took a hydro sample - gravity was 1.020, so I started the D rest.
The hydro sample tasted very good - I didn't detect any diacetyl, but I don't exactly have a trained palate. I decided to go ahead and do the D-rest as I figured it wouldn't hurt anything, so I raised the temp. setting to 62º F (another question - I've read D rest temps should be anywhere from mid-50's to as high as 68º F - I split the difference). On the morning of the next day (ninth day after pitching) the airlock was bubbling once every 6 seconds, but then later that day there were no bubbles at all (it's still air tight because I can squeeze the Better Bottle and change the level in the air lock). No bubbles since then - not one! No, I haven't taken another hydro sample yet - I don't want to do that until I rack it to a keg for lagering - I'm trying to avoid oxygen exposure.
I'm assuming fermentation is finished (expected FG is 1.013), but I'm just surprised at how suddenly the bubbling stopped - I'm used to ales where the bubbles slow down gradually over a period of days. And yes, I know people say that bubbles don't mean anything, but for me they've always been a good general guide for how active the fermentation was going.
So my questions are:
1. Is this sudden and complete cessation of activity normal?
2. Assuming I have reached FG when I take my sample in another day or two, should I bother slowly ramping down to lagering temp, or just crash cool it?
3. Should I have aerated with dry yeast?
4. What is the recommended D-rest temperature?
Thanks for your help.
EDIT: one more detail - the krausen, which was about 3/4 inch thick during primary fermentation has fallen back - now there is only a thin tan colored film covering the total surface area - thin enough to see through in places.