the only suggestion i have would be to try it and be ready to rip it out and find a new pattern if it's really too complicated. i just finished a sweater that i will be frogging this week, because i didn't listen to the yarn/pattern/myself as i was doing it. i wanted to believe i could do it. i did it and i hate it, so the lovely yarn will become something else.
that said, i looked at the pattern, and think i can offer some insight. as far as the cables go on the front/back, look at the picture for guidance. the "center panel" cable is the more complicated than the "left and right side panel". i think the pattern writers are confusing things by calling them panels. but that doesn't matter.
start knitting the K4, p1 rib, and do that 14 rows as explained in the written instructions.
starting on row 15:
Letters A to F refer to rows 15 to 24 only.
Left, Right, and Center panels: Work from B (A) to F, D to E, then (larger size only) A to C.
what you would be doing, is starting at B or A, depending on which size you are knitting, and working rows 15-24 across the "r/l panel", then the "center" (this is B to F), then the "r/l" again (D to E), then part of "r/l" (A to C) for the larger size, so imagine copying the entire "r/l" panel and placing it reversed to the left of the center panel on the graph page.
to this point, you've worked 24 rows.
the pattern repeat box is telling you which stitches in each row to work for each size once you get past row 24, so look at the blue and the red, and choose the blue repeat for small or red for large. it's the same as saying start with A or B.
this part is telling you that while you're going to work to 122 or 130 rows, you start the raglan shaping at row 62 or 70, after working rows 25-62 or 70
Rows 25–122 (130): Left and Right panels: Work pattern repeat box once, then work Rows 25 to (62) 70 or desired length to underarm. Begin raglan decreases following written pattern.
the shaping has not been added in the chart since they didn't do a chart for teh entire front/back. this is saying you're going to work in the chart repeating the "r/l panel" until you start decreasing for the underarm. you work this in line with the center panel (which is described in the next pattern line), like rows 15-24. you follow the written instructions to make the decreases for the sleeve shaping.
Back: Work Center panel repeat box once, then work Rows 25 to 68 or 76 or desired length to underarm. Begin raglan decreases at underarm following written pattern.
Front: Work as for back. Begin raglan decreases at underarm following written pattern.
i don't know if this is of any help at all. i'm going to post this, and then re-read it again. just know that you work the side panels in line wiht the center panel, and just visualize one panel beyond the center panel that they didn't chart.
edited to make it a little more clear.
another thought, do you have access to a photocopier? it might be easier to make a few copies the chart and cut out the different panels, and lay them where they should go, then you could visualize the repeats and cut out the raglan shaping and any extra stitches to avoid confusion if you are doing the smaller size. then you could more easily transfer that to excel and wind up wiht a more reasonably sized, full chart to work from.