You would have an easier time if you avoided Photoshop.
Create an Export Preset that is:
JPEG, sRGB, 8 Bit, DPI.PPI is irrelevant.
Long Edge - 800 pixels
Add Watermark during export in Lightroom.
Name the preset Model Mayhem and go nuts.
yeah i would but the only thing is. my watermark is brush affect. kinda like i am stamping my watermark on my work. instead of it being a jpeg. on another image. so it wont be distracting. i only use photo shop as a 2nd editor now. and only for advance techniques like cloning, retouch or things that i learned from when i took photo shop class using cs3 back in school. now some students at my college use Lightroom and not photo shop. i know things that they dont. yeah i have added the watermark to Lightroom but not as a png brush. it would be cool if i could.
i did a lightroom 5 image test with a photo i did i took of a model. and it worked. the file size is
320 x 400 at 157 kb
i am able to upload it on my end. my model mayhem account. what i did was type in the 400 x 400 px on hight and width in lightroom and i did a preset file size as you said.
did I do the settings right? or should i do the long edge 800 px. they are asking for the file size to be greater than 200 x 300 px. and at least 7 kb
but all i did was type in the width and height. 400 x 400 px and it exported the file as 320 x 400 at 157 kb. that is right ?
It is doing what you asked it to do. I see nothing wrong other than you seem to be holding the images to a size smaller than MM will display. If that is deliberate you are fine.