Film scanning with a digital camera.

It really all depends on what quality level you want. It is possible to get really top-notch results using a DSLR, but this requires a lot of thought and investment of time and/or money. Getting a set up which will give you this level of quality quickly and easily is even harder/more expensive.

Assuming you don't want to invest this level of time and money, you can get 'good' quality results with reasonable speed and ease using a basic copy stand-based setup. A continuous light source such as a light box/panel can work well. Another option for the light source is one or two flash guns, which can also work well if you can find a way to diffuse the light evenly across the frame. Avoid anything which produces heat, as this causes film to flex.

The biggest challenge is holding the film flat and within the (extremely thin) plane of focus. This is extremely difficult to do perfectly, but a decent compromise solution is to use negative carriers designed for enlargers, which can be obtained for all of the formats you mention. Other options include flatbed film scanner holders.

Whatever you use to hold the film, you need to block out stray light from your light source to avoid flare and if you're using a continuous light source, you'll need to avoid any light falling on the film from above also.

With this type of setup, you will need to spend some time levelling, framing and focusing at the start of each work session, and also each time you change format. However, once set up, you can get through quite a lot of frames pretty quickly and get 'good' results in terms of capture. I say 'good', because getting absolute best results requires a lot of time adjusting level and focus to get it optimal.

It's a similar deal with post production - especially if you're doing colour neg. You can get pretty decent results using Auto Curves in Photoshop, but if you want really good results you will need to do a lot of work developing your own methods and approaches, or looking into ones other people have developed. In my experience there aren't any automated methods which give you great results every time.

It goes without saying that the camera and lens you use is important. Obviously a dedicated 1:1 macro lens is best. The better the lens, the better the results possible.

My own setup uses a Kaiser copy stand, glass support raised around 15cm off the base, with a mirror at 45 degree angle below, flash gun pointed horizontally at the mirror. A desk lamp can be moved in in front of the flash for focusing light. Enlarger neg carrier sat on the glass. I use shims to tilt the glass base (and therefore film) to match the focal plane. I have a piece of card with rectangular hole cut to block stray light from below. I tether the camera to a laptop and use live view to check focus across the frame.

With a Canon 5DS r plus Sigma 105mm macro (EX OS version), I can get results which match those from a Hasselblad flextight scanner with 35mm and 645. However, this takes a lot of work. To reduce the amount of work required I would need to reduce the tolerances and play in every part of the system so that the film plane stays flat and in focus on every frame once set up.

As I say, it all depends on what level of quality you are prepared to accept.