...Noob questions here:
1. Is there an effect that allows a sprite to grow larger or smaller?
Sprite scaling? You can scale layers - http://sourceforge.net/apps/mediawiki/c ... ons#Layers - and in the picture editor - http://sourceforge.net/apps/mediawiki/c ... ure_Editor - and yes, you can resize a sprite - http://sourceforge.net/apps/mediawiki/c ... tle=Sprite
2. Can you make actual 3D games in Construct?
As in Quake/Doom? No. Construct can't use 3D hardware acceleration. It does have a 3D box object, though, but that is all.
3. Can you make an FPS in Construct (2D/3D) easily?
Someone has created a crude Wolf3D-style maze using Construct. You might be able to get it to do a Wolf3D-level shooter, but that'd probably be about it. Construct has no support for 3D hardware acceleration like that.