Really, it depends on what you want the extract to do. If you don't need to convert sugars in steeped grains, you're fine to use the non-diastatic. However, if you're using adjuncts or other grains in which you want the starches to convert into fermentable sugars (without the use of diastatic barley malt), you need the diastatic extract for that purpose.
The real question with the extracts comes down to the flavor profiles they create. As far as I know, there is no real flavor difference based on diastatic power, but you might want to find out how they rate the extract and what the grist bill was that went into making it. For example, here in the States, you usually find extract grades delineated as Extra Light, Light (aka Pilsner), Amber, Dark Amber, or Dark, each created with different grains and applicable to different styles of beer. You can also usually find wheat extract and even specialties like Munich extract.
I'm not really sure where "High Maltose" extract comes into play, but looking around the web, it looks like it's typically referring to non-barley based sorghum or corn syrups, which can be used in brewing, you just might want to look more into the flavors you'll be deriving from them. Sorghum leaves a very sweet cotton-candy like flavor even fully fermented.
As for the invert sugar, sure, Belgian Candi Sugar is an inverted syrup, and has been used in brewing for centuries.