It's hard for us to tell you which way you should go, I can just tell my own experience which might/will not fit you future experience or other people experience.
I would go the DSLR way, I did tried long ago and it was even better than expected, but I have already DSLRs and quite a lot of lenses.
Because I'm more on a prime lens side I would recommend the EF 100mm f/2.8 Macro USM, I have it for more than a decade, it's a fantastic lens, I use it in a FF camera (5D mark II and III yes my cameras are old but still fantastic)
Now for an every day camera, you will be limited with a 100mm which on a crop sensor will become like a 160mm (for canon multiply by 1.6 for EF lenses on cropped sensor), thus I think a Canon EF 24-105mm f/4L (I have the first version EF 24-105mm F/4L IS USM) would fit your every day (the aperture is not that big for portrait, but it does the job), it's also a "Macro" in a sens that it can focus at 45cm thus you can scan your negative with it.
On the other hand if you buy a cropped sensor camera like the 850D, I would look into EF-S lenses like the one you've mentioned, EF-S 18-135mm f/3.5-5.6 IS USM Lens, not sure it's a good idea though, because I don't like the range (a bit to big) and the changing aperture (3.5 to 5.6) while zooming, to be a good lens I suspect that this lens might have too much barrel distortion/color fringing... ➤ BUT I don't know this lens at all, so read reviews, it might be a fair lens.
In the end, IMHO chose the best lens you can afford first (might be any brand), then put a camera behind, a cheap DSLR will do a good job, because cameras can't break laws of physic ➤ before to hit the camera's sensor, the light will always pass first thru the lens, thus a good lens = good clean light = well lite sensor = good photo.
I would go the DSLR way, I did tried long ago and it was even better than expected, but I have already DSLRs and quite a lot of lenses.
Because I'm more on a prime lens side I would recommend the EF 100mm f/2.8 Macro USM, I have it for more than a decade, it's a fantastic lens, I use it in a FF camera (5D mark II and III yes my cameras are old but still fantastic)
Now for an every day camera, you will be limited with a 100mm which on a crop sensor will become like a 160mm (for canon multiply by 1.6 for EF lenses on cropped sensor), thus I think a Canon EF 24-105mm f/4L (I have the first version EF 24-105mm F/4L IS USM) would fit your every day (the aperture is not that big for portrait, but it does the job), it's also a "Macro" in a sens that it can focus at 45cm thus you can scan your negative with it.
On the other hand if you buy a cropped sensor camera like the 850D, I would look into EF-S lenses like the one you've mentioned, EF-S 18-135mm f/3.5-5.6 IS USM Lens, not sure it's a good idea though, because I don't like the range (a bit to big) and the changing aperture (3.5 to 5.6) while zooming, to be a good lens I suspect that this lens might have too much barrel distortion/color fringing... ➤ BUT I don't know this lens at all, so read reviews, it might be a fair lens.
In the end, IMHO chose the best lens you can afford first (might be any brand), then put a camera behind, a cheap DSLR will do a good job, because cameras can't break laws of physic ➤ before to hit the camera's sensor, the light will always pass first thru the lens, thus a good lens = good clean light = well lite sensor = good photo.