There's nothing wrong with 6000 pixel-wide image exports. That's often what I do. As for setting the text correctly, you'll need to experiment a little to get the size you want in the image export. I don't know what size you should set because I don't know how big you want the text to appear. There is no way to set lineweight in SketchUp. There never has been. You can do that in LayOut, though and you can use Hybrid rendering so the lines in LayOut are vector lines and will generally be crisper in the exports. (Keep in mind that edges and text will become rasterized in image exports. If you export a PDF from LayOut that won't happen.) And if you use LayOut's Text, Label, and Dimension tools, you can set font size, lineweight for leaders and dimension lines and other properties to get what you want. You'll also be looking at paper space in LayOut so you can easily compare the size of the text with the overall dimensions of the exported image.