My sensei once said that the longer you train - the more bad habits you incorporate into your technique - so in a manner of speaking you will never do the techniques better/more flawless than now
My experience is, that learning Aikido one technique at the time, wouldn't be very effective. You would soon grow tired of doing it again and again - and some of the principles you need to learn are better learned from some techniques than others. I used to practice Karate, and we had a 'linear' way of thinking divided by gradings. For each grading there was a number of techniques and a kata to be done and we sort of believed that when the grading was over we 'knew' that particular technique. In Aikido I find that it is all a big circle of knowledge and understanding of principles, and we keep on expanding our insight within the circle - dot by dot covering a little more of the whole area. For a while we go in one direction - then turn around and work in another area and every new thing we pick up influence the way we do everything else. Off course we have techniques that we seldom do with 'newbies' and there are probably some that I don't know about - still being a beginner - and we have a number of techniques to show at a grading, but basically everybody practice the same, and we are judged upon 'the amount of area that we have covered'. This works well for me. I like working on my posture in Sankyu and find that it has improved my Irminage etc.
As reply to your questions: Usually we do about 6-9 techniques during a two hour training session. Sometimes it's to fast for me - sometimes it's just right
If you do it right - bokken work can be very hard for the inside of your thighs.
Those were my ramblings.....