Personally, I would not do a protein rest. I have heard too many people (including myself) complain of loss of body when doing a protein rest. Today's well modified malts do not need this rest. I would only reccomend the protein rest if using large amounts of unmalted grain and none of your bill is unmalted.
By decocting up to the saccharification temp you run the risk of missing it low especially if it is your first decoction (again, this happened to me). If it were me, I would do a single infusion at 154-155 and pull a decoction to reach your mash out tmeperature. This way you gain the benefits of the decoction (Maillard reaction's, etc.) but do not run the risk of under (or over) shooting the saccharification temp. If you miss the mash out temp, it is not a huge deal and can be corrected by adding boiling/cold water without effecting the mash characteristics of the beer.
Let the smack pack warm to room temperature, then smack, then pitch that into an appropriate starter. See Mr Malty
for that. If you are pitching the correct amount of yeast, I would drop the wort to 46F then pitch and allow it to warm itself to 50F for the fermentation. Doing this, you should not need a diacetyl rest, but go by taste on this. If you are not pitching enough yeast, pitch at room temp, wait for the fermentation to start and then drop the temp.
You may not need to do the ferementation for 21 days but that won't hurt. You can lager as long or short at whatever temperature you want, so upping it for the primary fermentation of the second lager should be fine.
Some of this is my opinion, some is what I have read elsewhere. Some good links: