Is #3 true?
See no reason why it can't be. Actually any finger may represent penis and things related to sex. See no reason why it can't be thumb in certain cultures.

Those 25 according to Russia:

1. Tipping. Same as in USA. Tipping (usually 10%) is considered polite and represent good manners.
2. Back seat. Can't say actually. Don't think there any strong bias towards any variant.
3. Tumps up. Same meaning as in USA
4. Laughting with mouth open. It's OK in Russia.
5. Calling USA "America". When you say "America" 99% of russians would think about USA.
6. Being fashionably late. Girls usually are late for a date to make boys wait for them a bit. Buisiness people prefer to be on-time or a bit earlier. Being late isn't considered fashionable.
7. Being on time on parties. If you're invited on a big party, hosts usually expect you to be 30 min - 1 hour late.
8. Having hand in pocket. Bit impolite. Not a big deal usually.
9. Using left hand. Noone cares.
10. Opening present immediately. People usually expect you to do so. It shows enjoyment, not greediness.
11. Wearing... on public. Noone cares.
12. Altering your meal. Noone cares.
13. Showing soles of your feet. Not a big deal. A bit arrogant though.
14. Keeping shoes on. When 3 months a year streets are covered with mixture of snow, water and dirt, keeping your shoes on in the house is very impolite. Usually there're carpets in russian houses that are hard to clean.
15. Drinking someone else's alcohol. Noone cares.
16. Men showing skin. Noone cares.
17. Eating in places that don't serve food. Noone cares.
18. Telling people to help themselves. Not a big deal.
19. Touching. Not a big deal.
20. Keeping your clothes on in saunas. If it's a public sauna where men and women bath together you're expected to have swimwear on you. Especially when showers and/or pool are also for both genders. Most russians refuse to visit european saunas because of this no-swimwear rule. Especially women - they find it creepy.
21. Asking certain questions. Not a big deal.
22. Refusing food. Not a big deal.
23. Not declining gifts. You're expected to accept your gifts.
24. Polishing off meal. If you're eagerly cleaning your plate - that's not a clear signal for hosts that you enjoy your meal. If you do - ask for more)
25. Blowind your nose. Not a big deal.