I can tell you from experience that you need to ask the client at the very beginning if they have a preference regarding varying from the original line breaks. It saves time to know where they stand. Some will say, "You MUST do it exactly as written" because somewhere they have been taught that you MUST keep the line breaks and there is no changing their mind. Others will shrug and say, "Oh, you just do what looks best." I hardly ever had people in the middle. The responses were usually one of these two.
Many people expect the calligrapher to be the expert on all kinds of things - they will gladly dump all the decisions on you. Others have very specific notions - and sometimes you have to decide what to do if their notion seems contrary to anything you would do. If you think it will look awful, you should have ways of asserting yourself because it is very awkward to let someone talk you into doing something that you don't like and then having them walk out the door with something that you wish you had never done. You have to be very diplomatic about turning down ideas that do not fit with your views.
With regard to rough layouts, it is nice to have a set of fonts that approximate the different styles of lettering that you offer. Often times people will contact you by phone and you can ask them to send you the poem in an email. In just a few minutes, you can compose some roughs using different fonts and different layouts - and send them back in an email.....much faster than doing anything by hand. I can't think of anyone I know (of the old-timers) who does not use computers and calligraphic fonts to do rough layouts. Yes, the kerning or spacing will be a little different, but the fonts are close enough for step one. Often times, step one is the client choosing the font. If you offer several styles, it can be hard for them to know which one to choose. It is helpful to click through and see the same general layout in different fonts.
NOTE: you have to save your computer layouts as a PDF. The client will not have the fonts - so if you just send the doc - it will look bizarre.
Everything I said about having the client approve a proof (in the *crisis* thread about who is responsible for proofing) - insert that here. When they send the words - and you send the layouts, be sure you go through the steps to put the responsibility for proofing on them.