I've been playing about with tortoise svn and have a few questions.

In the case where I have created a trunk, and then copied that to a branch, modified some files in the trunk, and commited those trunk changes.

Case 1:

Step A) I merge from trunk to branch using "merge a range of revisions" with the "revision range to use" left blank, all goes well and I see the latest chnages from trunk in the branch, with the branch folder now having the red icon as expected. I then commit those changes in the branch and the branch icon turns green.

Step B) Without modifying anything, I thought I'd see what happens if I try merging from trunk to branch again. I expected nothing to happen as no further changes have been made. Yet, merging from trunk to branch again with "merge a range of revisions" with the "revision range to use" left blank causes the branch icon to again turn red. I didn't expect this, as no files have been changed. If I right click the branch and view "check for modifications" I see that the folder has a "property change"?

Case 2:

If I do the exact same thing, but this time not leaving the "revision range to use" blank, but instead selecting the revisions where the files changed. Step A) gives the same results, but Step B) now works as I would expect, in that the branch remains with its green icon and there are no changes.

Can someone explain the behaviour in the first case?

secondly, if I'm wanting to periodcially merge from branch to trunk, should I be using "Merge a range of revisions" or "Reintegrate branch"?

Before I answer this, do you actually need to be using an SVN repository? (Or are you just trying out SVN?). Unless you have an existing codebase + SVN repo, using Tortoise GIT would be a much better alternative (and use Git for the repo). SVN is fairly unpleasant when it comes to merging branches, and often has a few quirks in the process (which by the looks of things, you're starting to hit). For the second question, I'd personally use "Reintegrate branch" for a feature branch (and leave the trunk in as clean & stable a state as possible).