Do I really need an external camera flash?

If you have to ask this question, then the answer is probably 'no', you don't need one.

Pop-up (inbuilt) flashes are a small light source, which makes them 'hard'. They are also on axis (in line) with the camera lens, which gives them a frontal light.

Both of those things combined gives a flat, hard look to your subjects - like a 'rabbit in the headlights' look. It's the kind of lighting you have on your passport/driving licence photo.

It's not very flattering.

An external flash has the following advantages;

- it's a bigger light source. Bigger light sources give you softer light.
- good external flashes are bounce/tilt-able - this means you can direct the light to 'bounce off' a nearby (neutral) coloured surface. This, again, makes the effective light source even bigger (& thus even softer)
- the light is more powerful than a smaller, inbuilt flash (in terms of output & 'reach')
- it also can recharge quicker, for multiple shots
- it can also be used OFF camera, with radio triggers to fire it, thus giving even more possibilities in terms of lighting quality & direction.

Generally speaking, those who claim not to like flash photography are those who don't know how to use it properly. With skill & knowledge of lighting, you can make big, beautiful, soft light with flash.

If you want the best option to avoid redeye...then yes.

Not unless you know that you need them. In your case, it's obvious you don't so why bother?

You need an external flash if you find that the built-in one is insufficient or problematic. Don't worry, when the time comes, you'll naturally know when and then you'd wish you bought the external flash earlier. Don't buy yet though. You don't need it yet. A lot of people survive without even knowing what an external flash is.

Indoors I find bounce flash to be very useful.

Probably. But get one that has a head that can bounce light off walls and celing and also have a diffuser attached.
For better available light shots just get a reflector:
https://www.essentialphoto.co.uk/product/pixapro-5-in-1-collapsible-reflector-100x150cm/?gclid=CJWxmayghswCFY8y0wodR9QD2A

it depends on the type of photography you are doing.

Depends on you . You can control the light much better . The Nikon SB700 has filters for different kinds of indoor light .

There are two good reasons for an external flash. The first is that it is much more powerful, so will provide a better illumination of a big room or at a distance. The second is that it can be directed: flash illumination bounced off the wall or ceiling will provide a much softer light without sharp shadows. You are also less likely to have red eyes spoiling the portraits.