You mention shooting more macro and there are special flash considerations for that.
I shoot with Canon gear, but it's little different than Nikon when it comes to flash. I use several standard flash and, for macro, a twinlite and a ringlite.
My ringlite has a guide number of 14 meters and is a two tube design, where I can set lighting ratios (left/right or top/bottom, depending upon how the ringlite is mounted). I don't care for ringlites for low magnification work.... to me the light looks too flat. I mostly only use it for rather extreme magnifications such as the following shot of a newly hatched snail at about 3.5X life size magnification....
That snail was about 3 or 4mm long and the lens used is Canon's ultra high magnification MP-E 65mm (minimum of 1X and up to 5X mag). I used 8:1 light ratio setting of the MR-14EX Ringlite. Lens was set to it's smallest possible f/16 aperture (in search of even a little depth of field, since focus stacking wasn't possible). Because this is not an internal focusing lens, at high magnification such as this, f/16 is more like an effective f/64 or smaller aperture (lens at full 5X makes for and approx. f/90 effective aperture). So some added light from the ringlite is helpful, but this is typically the only lens I use with it, since all my other macro lenses are 1:1 maximum (unless extension tubes or a teleconverter is added).
The Canon MT-24EX Twinlite I use is more versatile. It uses two heads each of which has 24 meter guide number and, like the ringlite, allows the light output to be set up with as much as an 8:1 lighting ratio. Here's a non-macro but close-up shot where I used it....
Amaryllis blossoms are fairly large, so above what shot from some distance and the twinlite served as fill.
Twinlites are fairly bulky to carry around and use. I have modified mine, using a dual flash bracket instead of the original mounting that attaches the flash heads to the front of the lens. This gives me more versatility positioning the flash heads, but makes it even bulkier. Here's the twinlite/dual flash bracket rig attached to one of my DSLRs (left) and, a little more but still not very compact, attached to the lens in the original manner (right)...
Twinlites are more versatile than ringlites, IMO... but still are rather specialized.
It is possible to shoot macro using a single, standard flash, such as the SB700 you're considering. When I don't have one or another of my macro flashes with me, and an unexpected macro opportunity presents itself, I often use a standard flash that way. Following are some examples that were shot using a single, standard flash with 55 or 58 meter guide number...
The garden spider and turtle were shot using the flash as fill... the praying mantis was shot using the flash more full, in order to make a busy background go completely black. The garden spider was shot using a non-macro (max 0.21X) 70-200mm zoom with a 25mm extension tube.... while the other two were shot using a 100mm macro lens.
There are a couple tricks to using a single, big flash for close-up/macro work. The biggest problem is that the flash is too powerful and will completely blow out images at short distances. To deal with that, I carry some plain white gauze bandage and will put two or three layers of that over the flash head, held in place with a rubber band, to strongly diffuse and "hold back" the flash. When shooting small subjects up close, this makes the flash act like a "giant soft box" that does a pretty darned good job wrapping light around the subject (see the praying mantis example, where the flash was almost the exclusive light source, off to one side and above the subject).
If the subject is a cooperative one, with a single light source such as this it also may be possible to "bounce" some of the light using reflectors or cards, to open up the shadows a little.
The other thing is that you generally can't leave the flash in the camera's hot shoe when using it for close-up/macro work. Unless the flash tilts downward a little, it will not correctly project the light onto a very close subject. It's also often preferable to have it off to one side and higher up, maybe a little farther from the subject than the camera. To accomplish this, I use an off-camera shoe cord and simply hand hold the flash where I want it.
Here are the above "tricks" in place on one of my cameras and standard flash....
One of the advantages to using a full size flash this way is that you'll then have it with you for non-macro, non-close-up purposes.... for more standard uses where the twinlite or especially the ringlite wouldn't do... without investing in and loading yourself down with multiple types of flash units.
With all three types of flash, I use flash auto exposure almost 100% of the time. Can't recall the last time I used fully manual flash exposure (I do use manual studio lighting, usually set up using a separate, handheld flash meter). Canon calls it ETTL or ETTL II and it's metered through the lens. I imagine it's similar with Nikon, who I think call it "iTTL" or something like that. In this flash mode, when a Canon camera is set to M (without Auto ISO), the flash will fire FULL. This was used for the praying mantis shot above, where I wanted the flash to overpower ambient light, so that the flash became the primary light source. Alternatively, set to any of the auto exposure modes, the flash will fire as FILL (A/Av, S/Tv, P or M with Auto ISO). This reduces the flash's output by 1.66 stops, approx. and is what was used for the amaryllis flowers, spider and turtle shots above, all of which use ambient light as the primary source and the flash to supplement it. Regardless whether it's used as FULL or FILL flash, the flash set up this way still makes for auto exposure (in a sense, it even makes M an AE mode). In both cases it's possible to dial in plus or minus flash exposure compensation as I see fit.
Hopefully this will help you make a decision what's best for you.
EDIT: Several have suggested and there are some pretty good and considerably more affordable third party flashes that you might consider. I use OEM Canon flash and think they're better built, more durable (never had one fail), may have more features and am assured to be fully compatible with my cameras. I imagine the same is true with Nikon flash. But I know a lot of people are happy with some of the third party options too... They're definitely worth considering and some might even offer interesting alternatives that the OEM manufacturers don't (for example, compact LED light panels).