Help with brewing my first Blonde Ale....

IMO, for a first brew, I would stick with the kit as packaged; don't start adding anything to it. Concentrate on your procedures, get used to the physical acts of making beer than adding to a ready made recipe. There's plenty of time for that later.
The big things to keep in mind for your first time are sanitation, sanitation, temperature control and sanitation. Getting as much wort to a good book as you can, then making sure the yeast are happy and comfy will get the best beer you can make, and keeping unwelcome buggers out will make it that much better.

 

Well it sounds like you are off to a decent start. I have made 2 kits from more beer and have been pleased with both of them straight out of the box. I would brew it as is to start with and definitely would not try more than one additional ingredient. That being said it shouldn't be difficult to add coriander and would probably make a more distinctive brew. I know there was a thread not that long ago talking about the type and amounts of coriander people used that you should be able to find by searching. Final note on the honey/agave is that they will not add any sweetness as the sugars are simple and completely ferment out. I understand the flavor you can gain from honey at least is due to volatile compounds which will boil off, so I think many people add honey either after the boil, or in some cases after the first 24 hours of fermentation.

 

That's a pretty wild interpretation of "How To Brew." Nowhere does Palmer suggest adding anything at all for your first brew. He does talk about using fresh yeast, and perhaps following his process, rather than the often lousy process specified by the kit's recipe sheet.

My advice: Brew with the ingredients that came with the kit. You can always experiment after you know what you are doing. And read "How to Brew" again.

 

The directions with the kit are not always perfect, that is definitely true. But, the recipe is usually just fine. Brew the beer as is, but follow Palmer's instructions rather than the kit's. Save the experiments for later, when you already have a decent homebrew to drink in case of failure.

 

The key word is sometimes. It depends on who writes the instructions. More Beer has been making good beer kits for a long time. You can trust these guys. I understand the desire to adventure. I recommend suppressing it and brewing the beer as is because you probably have a much better sense of what a straight blonde should taste like and it will help you trouble shoot. Adding agave , honey, orange, coriander, etc probably makes it more difficult to diagnose problems. If you really want to do this, I recommend tracking down the instructions for a recipe that uses these ingredients and doing your best to emulate its proportions and timing. The hyperlinked recipe might be a good place to start to take care of the coriander and orange.

I would add 1 # of honey midway through the primary, or 1# agave at the end of the boil. Not both.

I do not recommend different extract or hops. Honey, coriander, and orange is plenty of ingredient tweaks to this kit already. The ultralight malt and the mild hops are the best bet for actually tasting the other ingredients.