My first mead mead- Strawberry Mel ?'s

Congrats on mixing up your first batch!

First I'll mention some general pointers. Most of us here don't boil our musts; it's unnecessary from a sanitation standpoint and can subtract flavor & aroma compounds from your mead. Acid blend is also something that is not recommended. You can add it at the end of fermentation to get the flavor to where you like it, but adding it up front can compromise the yeast by dropping the pH too low.

Ok, so to your questions.

1: IMO the extra yeast won't help at all. 71B is not a yeast used for sparkling wines anyway.

2&3: Bottle conditioning (to create natural carbonation) works like this: some sugar (which is usually added at bottling time) is fermented after the bottle is sealed. This creates a little bit more alcohol and CO2; the CO2 is trapped and you get carbonation. The best way to do this is to use a Champagne yeast strain (Prise de mousse, Epernay, etc) and create a dry mead. At bottling, a measured amount of sugar is added such that the desired amount of pressure is created in the bottle. The Champagne yeast strains are hardy enough to ferment the extra sugar. I don't know much about the Wyeast yeast you used, so I can't say how it would perform under these conditions.

4: Yes, the final gravity is probably enough to know if you're in danger of blowing anything up. You're looking for full attenuation (no sugar left) before you add sugar and bottle. If your mead stops fermenting at 1.010 (for example), it's probably not a candidate for a sparkler. It would be likely that the yeast is too exhausted to eat any more sugar (so it will be flat).

5. Sparkling mead is a pretty difficult thing to produce. Since this is your first batch, I would recommend letting the mead fully ferment and not worry about sparkling. Once you're more comfortable with the process and the results, you can revisit the sparkler idea and we can help you design a mead that will be perfect.

One last question: how did you get 20 lbs of berries plus 5+ gallons of mead into a 6.5 gal carboy?

I just thought I'd add a little advice to the bevy that AKueck gave. You didn't mention whether you did this or not, but it's good to aerate the must during the first 2-3 days of the fermentation to give the yeast enough oxygen to have a healthy culture. As for the sparkling bit, it depends where your final gravity winds up. If it gets all the way down to ~1.000, you should be able to bottle condition by adding some honey. A quick search on priming should get you the information for quantity to add for that. Personally, I hate bottling batches that are that large. If you have access to kegging equipment, it's a much easier just to force carbonate. Some may consider kegging less classy, but it's an awesome feeling to have a magic lever that gives you mead. Hope it turns out well!