It’s a lovely design and pretty color combination.
#1 The bowing on the side may well block out. Alternatively you might consider a wider border or a slip stitch border. The slip stitch would help even out the edges.
https://www.youtube.com/watch?v=LnP0MUgOzWo
#2 You would probably be best served by tinking back or ripping out to one row before the mistake and then tinking the last row. If the mistake is an edge stitch it takes a bit of time to ladder down fix it. Rip/tink is the easier solution.
If the mistake is a stitch or two in from the edge, you may well be able to ladder down to it.
#3 If you were to go with an I-cord edge, that is a neat way to hide the carried yarn. If not, then it would be better to cut the yarn and weave in the ends rather than carry up for such a long distance.
https://www.youtube.com/watch?v=9lVisnXB4_8
#4 I’m not sure that the plan will give you the look that you want. Double moss and seed stitch are most effective over a larger number of sts, say 5 or 6 at least at the edges. The very thick yarn would make a slightly wider border more effective.