There are plenty of codes that cover bathrooms from the allowable clearances for toilets, vanities, tubs, ceiling heights, ventilation, anti scald protection, proper waterproofing for wet areas, etc. You can Google the NKBA bath planning guidelines for some assistance with that as they are really too numerous to list in a post. Also read the Bath forum here for many of your questions. Posting your scale layout in the Bath forum will let others help you to see if you are following the requirements.

There are other common sense precautions to take as well such as not choosing a polished tile for flooring in a wet area, making sure that you install blocking behind the walls now in case of future grab bar installation, choosing a comfort height toilet, having enough towel bars at the correct locations, not choosing a porous tile unless you are prepared to keep it sealed and baby it, etc.

Then there are all of those little luxuries that you didn't even know existed that you now have the opportunity to include in your new bath. By no means am I suggesting that you order the 9K Inax toilet that will play you music and offer bidet functionality with remote control, but there are many things that can make your life easier and more comfortable. Or prettier. Like bidet toilet seats, towel warmers, heated floors (THE best!) fog free mirrors, shower niches, super quiet bath fans, and low iron super clear glass enclosures for tubs.

Read the planning guidelines and the Bath forum for a couple of hours (or days!) and then see if you still have unanswered questions.