Downloading ELF process failed "how to remove unconstrained paths"

1. In your case the unconstrained paths warning is not an issue, since switches and LEDs signal are not timing critical and there's usually no point in constraining them. You can simply ignore the warning. If you want to get rid of these warnings you must explicitly tell TimeQuest to ignore those paths or place some fake constraints.

2. altera_reserved_tck, as you can guess from the name, is a reserved clock automatically generated by Quartus for special functions. IIRC is used for managing jtag circuitry. This is unrelated to your main 50MHz clock, so you can cut the paths between them

3. This is very strange. Your sdc file should declare a create_clock to define your main clock net. Did you assigned it the name "altera_reserved_tck" ? That's would be wrong since another clock with this name is already implicitly created, as I said above.