Hi Scott

Thanks for posting in the Lucidchart Community!

The most straightforward way to do this would be using the "Set Default Style" option on the Edit menu (or when right-clicking an object). Get a line looking the way you want, then select it and pick Edit->Set Default Style. Repeat that same process with an object. This will make it so that your line color, fill color, rounding, etc. for any future lines or shapes will match your optimized example line and shape.

It is not possible to set default shape dimensions for a specific object type by doing this, but you can create a custom shape that has the dimensions you need following the instructions in this help center article.

Please let me know if you have any additional questions! 

Can I delete a custom template on Lucidchart (self-made template in the personal section). If not can other users see my templates? 

Hi Lara

If you created a personal template in your "My Documents" page and you have not shared it with any other users it should not be accessible to any other users. If you wanted to delete a template you can do so the same way in which you would delete a document. Right-clicking on the template/document or clicking the three-dot menu to render the "Move to trash" option.