converting handwritten notes: analogue to digital conversion?

Scanning is really going to be preferable to taking photos. The problem with the latter technique is that you have to ensure that the "film plane" (ie, the digital sensor) is parallel to the paper, otherwise you may have issues with part of the page being more out of focus. If you are willing to set up a camera on a tripod and get it aligned properly, then you could snap off a bunch of photos fairly fast, but it may be simpler to just use a scanner.

Regarding the format, either way the files are likely to be large. With a jpeg, you can easily scale the image down to wherever you can find an appropriate balance between size and readability. That's less easy with a PDF. Your scanner software should be able to produce a jpeg instead of a PDF.

what kind of post-photo modifications would you suggest insofar as minimizing the file size and helping to make sure that the resultant pdf is still "navigable"?

I would reduce the resolution to 72 dpi if you only plan on viewing those images on screen, and reduce the pixel dimensions as far as possible without compromising readability. That will reduce the file size as much as possible.

how would I go about "concatenating" the individual photos into a single document

Preview will do that, but it's a bit clunky. You can open all the processed jpeg files in Preview at one time, and it'll open a window with all the images shown in a sidebar. Select all of them there and choose File -> Export Selected Files, and choose PDF as the format. Now close that window, and then open all the exported PDF files. You'll get a similar window. Select all the images except the first one, then drag the group onto the first image. When a green circle with a + symbol appears, drop the images, and it will add them as pages to the first document. (Make sure you remember which one you're adding them to, since it will simply save to that file.) You may need to spend some time reordering the pages after doing that.

There may be better tools for this purpose. I don't do this sort of thing often, so I just use Preview.

You could try Graphic Convertor. It is designed specifically for the Mac OS to do all the things you are talking about. It has a lot of information in its manual about the different image file types and what you can do with them. There is a learning curve and a lot of it is way more technical than my level of understanding or interest, but the functions you are looking for are relatively simple, once you hone in on them.

I think there is a free or trial version of GC, I can't remember now, but the paid version is very inexpensive, and it is constantly being updated by its developer, lemkesoft. Adobe Photoshop Elements is supposed to be good, but very expensive, and there is no trial version for Mac, and in general the Mac versions of programs originally designed for Windows don't work as well or have all the features of the Windows versions.

If you want to check out Graphic Convertor, I would look for the "convert and modify" function in the file menu. Once you are in there, you can find the folder you want, and select as many image files as you want, and select functions to apply, such as saving WWW ready, converting to another file format, changing the resolution or size, renaming, adjusting/correcting brightness, contrast etc.. There is a way to combine jpgs into a "data stream" and to create multipage tiffs, but what I have been doing is saving things as tiffs, sorting them out and then converting them into multipage pdfs.

One thing I learned is that it is better to initially save images as tiffs, as that is the only common format that is not compressed. jpeg, png, gif, pdf are all compressed, which means that every time you open and save them, they get compressed again, which means you lose data every time you look at them. If you save them as tiffs originally, the file sizes are large, but you can pick which ones you want to be sure not to lose anything to keep as tiffs, so you can go back to them later if you need to.

You can select whatever level of compression you want for jpgs in Graphic Convertor, but there are so many choices it's hard to know which options to pick.You can save jpgs etc without compression with certain settings but the file sizes can still be large. There are different resolutions recommended for diffent kinds of images, for instance a line drawing should have a higher resolution than a typical photograph - the opposite of what I would have thought. Some of the high file size in multipage pdfs etc are not the image itself, but the digital instructions behind the scene so to speak - sometimes I've saved a jpg or a pdf with more compression to reduce the file size, but it ends up larger than I started, because what I told the program to do with it is saved with the image. You have to know what settings to pick to not save or get rid of that extra stuff if you don't want it.

The method described above in Preview may suit your purposes better - it's not that clunky once you do it a couple of times. You can also adjust the image size and contrast etc in Preview, and it works pretty well for the average user. One advantage of GC is the filters. One problem with using a camera for documents is getting the lighting even so there isn't glare on one part and shadows on another. This can interfere with readability. If you are adjusting the contrast etc in a program such as Preview it applies to the whole image, so it may improve one area and make another worse. The filters in GC can correct for uneven lighting to some degree.

I think there is a significant learning curve for all image processing programs. What is quick and intuitive to the eye is laboriously constructed and organized bit by bit in the digital world. If you don't want to spend a lot of time on this, I would really consider just getting a different scanner. I know exactly what you're talking about with scanning, but it doesn't have to be that way. There is better technology out there now.

If you're just scanning documents, the Fujitsu Scansnap scanners are amazing. You can get a portable one to do one-side scans for about $100, very good quality. You can select the file type, adjust the resolution/file size etc before you scan, scan directly to a multipage file, email, etc, without too much fuss. If you can afford it, a better scanner will save you a lot of time and aggravation and you will come out with a more useful and readable product. If the Byzantine world of image processing interests you, go for it.