TurboCooler

I know I can go to a ruler and drag and place a guide.
However, if I want my guide to be exactly 3.5in from the top, is there a way to type that in?  Otherwise, I have this guide that I cannot precisely place.
My mouse is not sensitive enough to get it exactly where I want it.

Illustrator has a tool called Live Trace that can convert a raster image into a vector one.  Is there a similar option for Affinity Designer?
Wonder if there is a way to accomplish this or if this a possible upcoming feature?

I want to draw a series of straight lines.
 
In other drawing programs you could often hold a key while using a pencil or pen tool and it would always give you a straight line.
 
Is there a similar concept?

Well there is no dedicated wide tool like in Ai where you can directly grab a point handle and adjust from there, instead there is the pressure profile panel (shown above by Pšenda) where you can adjust the line shape from. - See this explanation video:
Affinity Designer Line Width

Pressure?

Hey Fiona, 

Affinity uses something called Power Duplicate which is similar but not quite the same as the replicate feature I think you are referring to. Here is a quick tutorial that you can follow. 

Hi TurboCooler,
Welcome to Affinity Forums :)
You have to click on the last icon first on the Align Horizontally or Align Vertically section then untick Auto Distribute for the field to become available.

I want to draw a series of straight lines.
 
In other drawing programs you could often hold a key while using a pencil or pen tool and it would always give you a straight line.
 
Is there a similar concept?