Dad had me doing a lot of crap all weekend. Sorry. D:
Can monsters reach towers not directly placed in their path? Or will they ignore them unless you actively build a roadblock?
Yes. Some can only hit a tower that's right beside them (or 1 range, if you will). One creep type, however.... I don't quite understand the roadblock part though; you can't build on the path, so a roadblock is impossible. <_<;; In other words; most towers will be attacked constantly. Don't worry; early creep/minion waves won't do that much damage, plus upgrading towers brings them to full health anyway.
Is it possible for me to switch Target to Machine Gun? Target's unlimited range doesn't comply with my bonuses of range.
Also, how does Range work? Let's say the range of "Mysterious Tower X" was 2 and was placed on D5. What spaces can it hit?
Range is exactly what it's supposed to be; it determines how far it can shoot. If you build on D5, you can shoot to D7, or F5, or E6, etc.
And go nuts.
So what do I do with gold?
The only thing you can do with gold right now is buy and upgrade towers. I'll bring up another aspect (implying I choose to keep it) with gold a little later.
It's also used for sending out and doing strange things with creeps/minions, but since you don't have any for use, I won't bring it up just now.