League-of-legends – How are mastery points earned

Currently the Answer is NO.

Once you click on "Save and Use" the masteries are saved to mastery page number X (Where X = 1-10).

I completely understand what you mean with using different summoner spells on the same champion role, so what I created was, different mastery pages for the same role each with a different combination of summoner spells, so for instance my mastery pages looks like:

The one last mastery page is left as a Configurable one during champion selection, so if someone else on my team has clairvoyance and I am playing a support champ, I can get instead of C.V flash or heal.

10 Mastery pages should be enough to customize your preferences.

EDIT:

especially since I then have to remember which one is "Mastery Page 4"

You can change the mastery page name by simply clicking the default name and when done hitting ENTER.

The League of Legends Wiki lists all of this. A table for the rewards for kills is shown in their Kill article, which I will mock-up below. Note that as of V1.0.0.152, the bounty values were reworked to increase the effect of each kill or death. The table shown below reflects the current bounty rewards as of said patch.

K/D Count = Killstreak/Deathstreak count for the champion slain
K Reward = Improved reward for killing a champion with that kill streak
D Reward = Reduced reward for killing a champion who is getting hosed

K/D Count | K Reward | D Reward
----------+----------+---------
    1     |   300    |   300   
    2     |   360    |   260   
    3     |   432    |   182   
    4     |   500    |   127   

The Kill article notes that a first blood has a +100 gold bonus, so the first blood will always be +400 (as this question leads me to believe that executions don't increment your death streak).

The other point to take home is that multi-kills and aces do not provide any bonus. Likewise, getting a killstreak doesn't get you any additional reward, only the person who finally takes you down.

The article for Assist states that there is a pot of 70% of the kill bounty that is split between all champions that provided an assist for a particular takedown.