1, yes, makes sure it is done. In generally you are pretty safe just letting it ferment for a week unless it is a very high gravity beer. Pay attention to the airlock. Once you are getting less than 1 bubble per minute, fermentation is pretty much done. On the whole I'd suggest letting it ferment for 2 weeks on the low end. Longer time sitting in the fermenter often leads to a better beer in the end, and you can be almost absolutely sure fermentation finished days ago. You always want to take an original gravity measurement and a final gravity measurement. If you are using a kit or recipe, it should be very close to what the range for OG and FG is. If it is way off, either something went badly wrong, or else fermentation stuck, in which case you should consider warming the beer some and re-pitching yeast. This doesn't happen often.
2) I've never heard that Grolsch bottles are stronger, but could be true.
3) You'll ruin the beer doing this. Increases odds of contaminating the bottles, you'll likely lose too much CO2 leading to a flat beer and odds are excellent that 90% of the fermentation is going to be done in the first 18-48 hours in the bottle, so you aren't gong to reduce the risk of a bottle bomb unless you are opening it very early (say after 12 hours or something). After most of the fermentation is done it takes the beer a day or several to absorb as much CO2 as it will. In general every 10F warmer or colder will double or halve fermentation rate (so if you bottle at 70F and then cool the bottles to 60F, it will take roughly twice as long for it to ferment and then carbonate, if you warmed from 70 to 80, it'll ferment roughly twice as fast).
4) It is the amount of sugar added to the entire batch.
In general you want to use between .75-1 ounce of sugar per gallon boiled in a small volume of water (and then cooled) and added to your bottling bucket. This will give you roughly 2-3 volumes of CO2 per bottle which is generally in the range of CO2 you want per bottle depending on the style of beer. Some styles call for a little less, like 1.5 volumes, some call for a little more (like 3-4 volumes for some wheats and fruit lambics). Most are in the 2-3 range.
Generally you are going to have problems once you start getting above 4 volumes of CO2. I personally wouldn't be comfortable carbing above about 3 volumes of CO2.
I wouldn't worry about it. The only time I have been seriously concerned about bottle bombs is my third batch, a caramel oak porter. I hadn't learned the trick to boil the sugar in water first before adding it to the bucket, I just poured the pack of sugar in and stirred. Well I didn't stir it in very well on my third batch so on the last 5-6 bottles I noticed some sugar slurry at the bottome. I stirred it in, but the last 5-6 bottles probably got twice the sugar of the rest. So instead of around 2.2-2.5 volumes of CO2 in the end that the rest of the batch ended up, these bottles probably got closer to 5 volumes. None have broken and I bottled 2 1/2 weeks ago. I did however place that six pack in to a cooler and closed the lid for the first two weeks.
Just to be sure.
I have had one bottle break on me, but it was a simple breakage, not a bottle bomb. Bottle feel out/broke out about a day or so after bottling. Likely a flaw in the bottle or a slight crack I hadn't noticed. An occasional, but rare, issue with using used bottles.
If you are that worried, place the bottles in coolers after bottling for a week or two. Alternately you can store them in a cooler place (the cooler the place, the more CO2 will be absorbed in to beer itself, reducing bottle pressure). I don't think you are going to want to store below around 55-60F for an ale, otherwise it might have issues fermenting and carbing. At least not until it has bottle conditioned for a week or two first to ferment and carb up.
Also you can place the bottles in to boxes to at least reduce the devastation a little if any of them do blow...not that I am making you feel better I am sure.
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