I was in Istanbul for 6 months making videos for YouTube and taking photos. I visited and photographed many of the mosques and Nuruosmaniye Camii is really special. I actually made a 360 video tour of it because I would hate to think that anyone may miss visiting if they went on a trip to Istanbul. You don't need a guide, the care takers are very knowledgeable and enjoy sharing information. There are also multilingual signs around the grounds explaining some of the history and purpose of this amazing building. If you want a grand experience though try seeing it for the first time this way.
Come around to Nuruosmaniye Camii from the square that houses the Column of Constantinople. As you walk through this very flat area towards the mosque you really get a feel for its sheer size. There is an old stone wall around the structure and you will notice it gets larger as you get closer but Nuruosmaniye Camii does not really grow in size much. When you get to the wall make a right and then a left. This will bring you to the back gate. Enter the gate and about 10 meters in on your right hand side is an information post. Take a good look around and be sure to look up when looking at the main structure. As you proceed down the path to the main entrance there are a lot of trees. The best time for seeing the actual building is in winter and spring. Really take a look at the construction though, the work was done with a lot of love and care. Once you get inside the main door its a massive room. The care taker did this cool thing where he closed the curtain over the entrance and the whole interior went dim. Then he opened the curtain and let the sun in. The stone I guess is reflective and the whole place lit up. The interior is very tastefully decorated. White marble, stained glass and dark accents. On the way out you can leave a donation if you like. I always appreciate that when I am making a video of somewhere.
I would suggest taking a day and just walking from the metro station towards Sultanahmet Square. You have Hagia Sophia, Blue Mosque and the Hippodrome of Constantinople at Sultanahmet Square. If you continue up the street, on the right hand side is the Tomb of Sultan Mahmut II (Googles name for it) and right after that is the Column of Constantinople. The column isn't a lot to see but right next to it is Bey Gummus mosque and through the square is Nuruosmaniye Camii. After that you can either hit the Bazaar or head back towards Hagia Sophia and check out Gulhane Park.