Potential problems ?

I brewed a Brown Ale on Saterday. First mistake was missing my mash temp - my thermometer read 152F untill I stirred after 20 mins and the temp dropped to 147F - I can only assume that the thermometer probe was sitting in a pocket of mash that had a higher temp. I added 1.2L of boiling water but it didn't help much.

My main concern was the taste of the wort post boil -it was very bitter instead of being sweet like the other beers Ive done. I stopped sparging at 1.010 and hop additions were as per the recipe :
2-row, caraamber, toasted oats, toasted 2-row (both lightly toasted).
Could the bitterness be from too low mash temp ?

Then - my fermentation bucket leaks slightly. I can tell by pressurising the bucket by hand - it gradually loses pressure.
Should I transfer to an airtight bucket ?

leave it alone, no need to ferment in a vacuum. most of my buckets leak a bit now and then, just keep using what you have until you can afford a fancy pantsy carboy and rubber bungs.

Will do, thanks. Its been bubbling away just fine. The bitter taste has subsided as well.