Hi! I used Game Maker before 3DGS as well and found that it really helped with understanding simple code, ifs, variables, simple physics etc. I also found 3DGS massively more complex, my problem though is the time need to make a 3d game as there is so much to do but aside fomr that... If you find it hard to start then simply go straight to the main character (player if you want) of the game. Try to get it moving, get the camera to follow it, build a simple world for it (i.e - floor , walls). if modeling is your problem then try tutorials else where. Once youve got what you want for a player start to work on other aspects of the game. get the basics out of the way first:

1. Player
2. Camera
3. Variables and HUD (Most importantly health)
4. Simple environment
5. Interactions between player and environment
6. Coins, items
7. Opponents
and so on

I tend to follow 2 different patterns
1. Make a test level and build EVERYTHING in that.
2. Make levels and work through them adding to the content of the game as you go.

Work on the much more complex and nittuy gritty things later, come back and make that pest lens flare or auwkward explosion special effect later because it isn't important.

In terms of coding I started pretty much ALL of my code by copying what I wanted from the 1st person shoot tutorial on Acknex. Once I started to grasp the basics I jumped into trying to do my own.

Basically: Start simple and do what you can do rather than trying to do crazy amazing things straight of because otherwise you wont get any where, I know from experience =P

Sydan