поди ж пойми = literally "go figure" that out Сидит птица на попе. = well, the bird does sit with its 'butt' down on some surface. so it kind of sits on its butt. though, the word 'попа' is not really a 'butt', it's a most soft word for that part of the body, mostly used with a small children or when you wish to sound extremely harmless and soft. that part of the body has a lot of various ways to be named :).

most likely you've a mistake in your phrase, it should be: я-то представлял себе.. (note the dash between я and то). in this case то is used to specify that it's precisely you who you do speak about. that it is you and specifically you were the one who (представлял) believed/imagined/etc я то представлял себе (with no dash) on other hand means that you did imagine THAT in some way... here то refers to something that is not yet mentioned in your sentence. for example: я-то представлял тебя иначе = me, my image of you was different я то представлял себе иначе = in my mind i imagined that thing not like that я-то думал, а он нет =me, i was thinking and he did not. я то думал, а он не то = i was thinking the right thing (that one) and he was thinking the wrong thing (not that one).

there are no rules for that. tongue position for soft consonants is easier in junctions with certain sounds, therefore due to the law of natural laziness foreign words get soft signs at times.

to be honest i don't even remember when the christmas is, only that it is in january.. :D

i don't know if you know that or not but in any case here it is. russians do not celebrate christmas in december, it's in january (orthodox church christmas). and second thing is that christmas in russia is a very small holiday mainly for religious people only. like a day of a miner or a day of doctors :). while new year is the biggest holiday of the year, so better congratulate your russian friends with a new year, it will make a lot lot lot more sense :).

да не то чтобы [это было..]=it's not that.. "Да не то чтобы неприятности, просто.." означает, что человек не считает происходящее неприятностями, но тем не менее и не считает происходящее чем-то противоположным неприятностям.

граница is a line between two somethings that separates them. предел is a top line of the possible for someone/something.