You have a lot of nice old stamps, and with nice cancels too sometimes.
The first, Russia, I think has some kind of overprint that possibly turns it into an Arrmy stamp of some sector. Not up on these.
The Great Britain King George V (KGV) has part of a slogan cancel probably from the exhibition (special stamps use that lion also) time frame. Lots of color shades of this stamp. The cancel probably says something like. . . British Empire . . .
The US stamp has the obliteration part of a duplex (two part) cancel on it. The first part would be a circular date stamp showing the town and date. This second part (oval or football shaped multi barred numeral cancel) shows a numeral that probably stands for the post office or depot in that town or the postal clerk? Not Sure.
The next, Austria, Oesterreich, nice perfin, well centered, some drift off to a side and ruin the side perfs, has a Praha (?) I think cancel (Prague, Czech Republic now), 30 Nov 1912, as shown in Europe, You can, with catalogues and web sites sometimes, find out what that perfin is. Like I said before, post singley on a topic and ask what you want to know. I know some things but am missing a catalogue so no numbers from me. Well, Canada and GB catalogues.
Most here is North America use Scott catalogues and the numbers from North American sellers will be from Scott. However, different countries have their own specialized and general catalogues. Gibbons is best for British Empire and Commonwealth stamps, being based in Great Britain. More detailed reference, showing errors and varieties sometimes, that Scott does not show.
Scott is better at showing US stamps. Yvert or Maury (I hear) are better at France and colonies. Michel at Germany and states and possessions and colonies. Unitrade for Canada but uses Scott numbers under lisence. Depends on how specialized you wish to get when collecting.
If collecting just s few countries it is worthwhile to get the specialized catalogues for some. You don't need to though.
I could tell you a number for a Canada stamp or a Gibbons for a GB stamp (that shows in my concise catalogue) and when talking to someone else, well,, they better have the same catalogue or the numbers mean nothing really.
The numbers you see in
ebay titles are catalogue numbers but probably different catalogues depending on who is listing the item and where they live, or even which catalogue they are using. If they don't state a catalogue maker then you can assume from where they live (Germany area = Michel) which catalogue usually. Or which is preferred by specialized collectors of that area also. Confusing at times.
Next two stamps are from the AustroHungarian Empire period from Austria I think. The Konig is King, Wein is Veinna, the names of towns might have changed over the years also. The dates are 1893 (I think) and 1890 or 1898? Not an exact science here. Day Month Year usually. The cancel will not always tell you the exact year either that the stamp was issued as some stamps had a long life of usage (10-20 years) but should put you in the general area.
Damage to a stamp can be looked at in different ways by different people. You can say, well I want a copy of this stamp and willkeep what I have until I find a better one. Or you can say its not good enough for my standards now so in the trash it goes, or I will trade or sell it. Its up to you what you do.
For display and competitions I would imagine no damage is acceptable at all.
Next stamp is Jugoslavia / Yugoslavia.
Cool pyramids on the Egypt airmail stamp. Post Aeriene is French for Air Post or Air Mail. In Scott these would be listed after the regular postage stamps in an airmail section. In Gibbons they are listed all together with the other stamps.
Sorry I have no idea on years or numbers again.
Last is France airmail 1935 (cancel). The names along the bottom on some country's stamps are the designer and engraver.