Welcome to GotMead Garrete!
You sound like you have some experience brewing, but even so, I suggest taking a look at the
Mead NewBee Guide as it does contain some very useful information.
I will also point you to the
GotMead mead making calculator - one of the most useful tools I have run across. If you play with it a bit, it will give you some good estimates for mixing your batches.
The wyeast strain you are using has an estimated ABV tolerance of about 11%. It does have a reputation for being persnickety especially if put into high gravity musts. It is not essential to use a starter, but it won't hurt.
Now for mixing up this batch, it will be helpful to use your hydrometer. I'm betting that you have one, but if not, it is probably the next investment you should make as it will help you more than anything else to monitor the progress of your mead, and to be sure when it is done.
Going back to the mead calculator, if you plug in the 12 Lbs of honey into a total 5 gallon batch, it predicts a starting gravity of 1.088 and your yeast tolerance (11%) is at about 1.080. This would mean your final gravity would be around 1.008 which semi-sweet at best.
If you plug in the 12 lbs with a total 4 gallon batch, you get a starting gravity of 1.110, which would leave you finishing at around 1.030 which would be very sweet.
So, you can make it semi-sweet to very sweet depending on what volume you decide in between 4 and 5 gallons. You dissolve the honey in some water, and keep adding water until the specific gravity reaches the number you want. I would not boil the honey or the must. Recognizing that you can always make it sweeter by adding more honey after fermentation finishes, I usually err on making it a bit less sweet. If your mead winds up too sweet, it is difficult to correct.
I would then add the DAP approximately 1 gram per gallon (or 1 tsp for 4 gallon). You can add another 0.5 g/Gal at the 1/3 point of the fermentation if you like. After adding the DAP aerate the must really well - I use a whisk. You will want to aerate the must daily for the first 2 or 3 days. This will help the wyeast to finish the job without sticking (hopefully).
I would not add any acid blend. This may drop the pH of the must too low, and stall the yeast. After your fermentation is complete and cleared, you can taste it to decide if it needs any acid added, and if so, can add it to taste at that time.
I hope this answers your questions, and please keep us posted on your results.
Best of luck with your mead!
Medsen