Wishing someone merry christmas

Q: If a Muslim wished someone merry christmas will he have become a kafir, because in modern times christmas is just another cultural money making thing and people do not know the reality of christmas that it is the celebrating of jesus birthday and therefore if a muslim said merry christmas at a time without realising at the time the consequence and value of what he was saying he merely just said it out of respect or he said it but out of regret then will he become a kafir at that point? Because a muslim could have said the words merry christmas but with regret in his heart, obviously one understands to not do such a thing again but will he have become kafir for saying this without truly meaning it ?

Washing impurity of the body

Q:

1. If some drops of urine get on the side areas of vagina even after all the precautions, does pouring water over them using Muslim shower during istinja is enough? I usually wash my legs separately, wash with soap and pour water over the area thrice as i don't get satisfied by pouring water while making istinja from Muslim shower. What is the right way? I read on your website somewhere that drops dont need to be washed..they can be wiped with tissues. Is it correct?

2. How many times water should be poured on napaak body part? Some says two, some says three. I use soap then pour water thrice. Is washing with soap necessary?

Seeing blood on one's clothing after performing salaah

Q:

1. After I had passed stool, there was a lot of bleeding in my back part. I wiped until I saw no blood on the tissue, then took a shower, then prayed dhuhr and asr prayers. Then at maghrib I went to the bathroom, and saw even more blood. Do I assume that the bleeding started again after I prayed asr, or do I assume that the bleeding was going on the entire time and therefore I have impurity all over me (because I showered) and my prayers are invalid?

2. Also, I often have bleeding in my back part and the toilet tissue we use is not clear white - it naturally has yellow/brown/red bits in it (I think it is because the tissue is recycled) and this makes it hard to tell if something is blood/stool or just the normal color of the toilet paper. If I wipe until the toilet paper comes back clean, then wash myself, then check again using toilet paper, however during the check I notice some spots that I'm not sure is normal color vs blood/stool, so I check again, but this time the toilet paper is clean, can I assume I am pure?

Performing qadha salaah

Q: I started praying five times a day. Now I realize that I lost almost 25 years of praying. So according to this I was praying all this month but not regularly so Ramadan regularly praying almost praying for other days as well morning. Was it as well so I feel almost 10 years has been done now remaining 15 years prayers out there so I calculated for 15 years. So I need to clear 5475 pending prayers it is just an approximately figure please suggest advise me on this one