Sure, and sorry it took so long.
In regard to the first paragraph, I can clarify, although some of this is going to be stuff you already know probably. One of the ways you are likely to find yourself using the modes is while improvising over a set of chord changes. For a given type of chord, there are typically one or more scales that "fit" the chord, some better than others. Not all of these are major modes, the modes of harmonic minor are also very interesting and prevalent in jazz, and there are other scales like the bebop that fit things, and a slew of others.
If you were improvising over a steady chord, a Bb minor 7, for example, the Bb dorian scale is one that would fit, and you could spend a lot of time playing licks based on that scale, triads, etc. However, most tunes that you play will be based on some chord progression. There are standard progressions l ike the blues, I IV I V VI I , and there are various other common forms and turnarounds in jazz. As a soloist or a melody writer, your goal should be to have your lines flow as smoothly as possible over these chord changes, rather that just noodling around in one scale for the first chord and then changing positions and noodling around in another scale when the chord changes.
So when you are taking a solo over a blues, for example, and the chord changes from C7 to F7, you don't want to have to shift yourself down to F and start playing the mixolydian scale from there. You could do that but it is not at all interesting to hear some guy noodling on a scale, particularly starting from the root. You can achieve a much more pleasing line if you pick up the next scale seamlessly on the chord change.
Lets say I have broken the previous rule and decided for my solo over a C blues just to play an ascending scale. The most common scale for C7 is c mixolydian, so I play C D E F#, and now the chord changes to F7. I want to continue my nice ascending line, so I consider F mix. for a second, and I know that going up from F#, G is the next ascending note that is in the F mix. scale, so I continue my line with G, A, Bb, C. The idea is that as these chords change underneath you, you want to be able to begin playing "inside" one of these modes. Because you might be starting someplace other than the root of the scale, the shape you memorized is no longer so helpful, what you really need to know is, when the chord changes, how can I get into the next scale from where I am now. This might sound like a complicated thing but it is how modes are actually used in practice.
Sometimes a composer will choose the chords such that a single scale fits everything. For example, if you wrote a tune where the chords were all the triads from the C major scale (CM7, G7, Bdim), then you could improvise with the same scale over every chord in the song.
Paragraph 2 means the same thing. When you are trying to learn these modes, what you ought to do is to practice playing around with the notes in the scale over a chord. Like say you're working on dorian. Use a keyboard or something and have it play you a Cm7 chord, and play the C dorian scale. Then play the 1, 3, 5, and 7 tones in that scale, then play them in various combinations, just listening to how nice they sound against the chord. Then try doing the same thing with two chords, say a Cm7 and an Fm7. If you write out C dorian and F dorian, you'll find they share some notes. Use keyboard or something to loop 2 or 4 cars of Cm7 and then Fm7 and just pick one of the shared notes and keep playing it as the chord changes, and listen for how it fits.
What you're really trying to do when you make up basslines is play pieces of a scale that fit a chord, and as the chord changes, you want to try to find the note that is closest to the note you're on now that is in the scale that fits the next chord, or possibly stay on the same note, if it fits both chords. There is no rule, other than that it should sound good.
In regards to paragraph 4, I already told you a way to remember the scales other than by rote

It's via the circle of fifths. Again, briefly:
Bb major, thats easy. C has no flats. To get to Bb from C we go past F (one flat) to Bb (two flats).
The flats, in order, are always: B E A D G C F (circle of fifths again). So if a scale has one flat, its always B. If if has two flats, its B and E. Three flats, B E, and A. etc.
So Bb major has two and theyre B and E. Bb c d Eb f g a Bb.
C dorian. Dorian is a whole step above major. Go down a whole step. Its Bb major! We just figured that one out- b and e flat. So C dorian is c d eb f g a bb c.
C# dorian. Go down a whole step, B major. On the circle of fifths, B has 5 sharps. Sharps, in order are always F C G D A E B. So B maj is B C# D# E F# G# A# B. C# Dorian? C# D# E F# G# A# B.
It takes about a second to figure out the notes in any mode this way, and all you have to remember is the circle of fifths which tells you not only how many flats/sharps are in a particular major scale, it also tells you what notes they are. A scale in the major modes with four flats will always have Bb Eb Ab and Db, etc.
Hope that helps!