Is a tailored device better for beginners?

Hi I’ve asked a few questions lately and the advice has been consistent: don’t just grab an off-the-rack model, but opt for something tailored to you. This seems even more important since I plan on wearing mine around the clock. a) Since I’m new to this, am I likely to mess up the measurements? b) When you order custom, should I expect there will be some tweaks needed? Thanks Barry