Various little nagging problems when trying to tune up a 3D printer

Hello to all:

I am trying to tune up a Stacker S2 3d printer using Simplify3D. It's a nice, good-size industrial machine and well-built, but it's giving me some nagging little issues:

1) Extrusion width. I am using I-Beam Impact PLA: 200 C Extruder, 100 C Bed. Filament sticks to bed great and lay-down appears to be good...but I've noticed that the first layer of the skirt is printing wider on the right side of the skirt than on the left.
2) Which way is best to control extrusion lay-down width? I've been changing the extrusion multiplier, but this sees like too arbitrary a way to fix my width issue.
3) I've been making small blocks/prints of buildings. I noticed when I took the parts off the bed that the edges show "sagging." I'm NOT saying the parts are lifting/curling up off the bed, that's actually one problem i'm NOT having AT ALL. It looks like the corners of the layers aren't lining up. And it's doing the EXACT same thing on two parts being printed in the same session, the edges of the layers are gradually bowing inwards, then back outwards, like what a rope-suspension bride looks like. The fact that i's doing the EXACT same thing on both parts suggests a parameter/software tweak of some sort is in order....
4) lots of stringing when trying to print multiple parts on the bed at once.

I've attached some pictures for reference. Thanks very much in advance for any help/advice! :)

There are a number of things you need to deal with to get a good print with the correct size and height.
1 Bed level (must be level within .02mm is what I shoot for)

2 Starting height must be correct, this is also call Z offset and is the height of the nozzle over the build plate during the first layer. You "should" want your first layer to be the same height as the layer height. S3D has a setting call first layer height that does different things depending on your version. Set it to 100%. There is also first layer width, set it to 100%. The offset must be set using a model of know height that divides evenly with your layer height. I use a 2 walled square that is 2mm tall for a .2 layer height and one that is 3mm for .3. If the staring height is correct this part will measure exactly 2 mm or 3 mm tall depending on which one I am using. +- .02mm is ok, and i normally shoot for .02 less to make sure I have good adhesion without an squish on the first layer.

3 Filament diameter, measure it in multiple places and in multiple places around the circumference of the filament and enter the average into S3D

4. Extrusion width. Set this either to auto or to less then 1.2 times the nozzle diameter. I prefer fixed width rather than auto. For instance, I set it to .4 when using a .35 nozzle and .5 when using a .5 nozzle.

5 Extrusion multiplier , this must be calibrated using a model and a caliper. The 2 walled squares I used to set starting height are also used as a first check of extrusion multiplier. These walls are modeled to be the same as my extrusion with. I have perimeter overlap set to 15% for this calibration so the walls will measure about .02 thicker than the model (for example a .5mm wall will measure 1.2mm (2 walls)
The final test I do is a one layer square which will let you see how well each tread is attached to the one next to it, there should be NO spaces between thread like in your photo. Again if the first 2 above are not dead on, you can not set #5 with much accuracy.

Having the ability to make your own simple models will make this process much simpler.
Hope that help and good luck!