Wiring – New light fitting coming on with wrong switches

First thing to confirm would be which direction the switches are being fed from. There are 2 ways that you can do this - feed from the switch:

Or feed from the fixture:

When feeding from a fixture, you'll notice that one of the white wires is actually being used as a black wire. It is common practice for this to be "coded black", usually with a single wrap of black electrical tape, but not everyone does this. By the description in the comments, it sounds like everything was being fed from the fixtures except for the porch light (although it seems odd to do a lamp post that way given the extra wire required, but I digress). My guess is that the box where the recessed light went was wired correctly, just using the bottom method from the 2 pictures above.

The second step is to confirm that the wire you have marked as "Service Box" goes to the distribution box. If it does, your previous wiring set up was probably like this (in which case there should have only been one wire nut in the box other than any used for grounding):

Until you do these two things, it would be premature to decide on how to combine switches or re-wire. You could reverse the wiring for the garage or lamp post to combine switches, but you'd need to figure out what to do about the hot running into the fixture (capping it may not meet code in your area). What you would basically be doing is changing from fixture feeds to box feeds and figuring out what to do with all of the fixture hots. Multimeter readings likely aren't going to be much help - pictures of all of the boxes at the fixtures would help more (or diagrams of each box with wire connections noted).

I'd start with confirming the wiring the diagram above, get the wiring back to how it was originally so everything works again, and then posting an update with the information above for advice on how to change how it is wired.

EDIT: Porch and lamp post can be combined like this:

You inadvertently bypassed the switch loop that controls that light fixture. There will most likely be a cable with a white wire that is not connected to any other white wire -- that cable is the switch loop in all but the newest installations.