Event Planning

For the three hour event on Sunday and Bulbasaur everywhere you will get XP x6 when using a lucky egg. Thats pretty much between 2000 and 3000 XP you will make per minute. For six lucky eggs you will then be able to make around 500.000 XP. Not quite as good as evolving for three hours, but a lot more fun fon sure with the benefit of not having to use your precious pidgey candy.

Using starpieces will be the same for the whole 2 weeks, assuming we will get double dust on everything. So it's up to you if you want, triple stardust instead of double.

If you plan to hatch something like 9 10 km eggs a starpiece could be a benefit. I will time my eggs, so that they hatch during bulbasaur event and use both starpieces and lucky eggs for the three hour time frame.

I think the XP bonus applies to all catches, not just Bulbasaur.

I'm planning to hatch some eggs. Have 39 lucky eggs. 33 premium passes. 10 star pieces. 1.5 million XP to 40. I wish I could play hard during this whole event, but like most other events I'll need to find the grind time.

I would (and am going to) use both lucky eggs and star pieces through the whole 3h of community day. Gregoire detailed quite well how it works for making exp and since you're concentrating on catching so many things, there's going to be a bunch of stardust coming in also, so the star pieces will be put to very good use.

Other than that, you should actively look for opportunities to use your star pieces during this event. The bonuses stack multiplicatively so your pieces are producing more bonus dust than they would normally ie. more bang for your buck.

3x XP: Applies to everything you catch, not just Bulbasaur, and only during Community Day.

Bonus Candy: Applies only for eggs and for all of the Eggstravaganza event.

2x Stardust: Applies for everying during the Eggstravaganza event.

Lugia: As far as I've read there's nothing that proves that raids are decreased during the event. Last Community Day I only saw one T5 raid, but that could easily have been a coincidence.
I personally think that having a few raids during the event would be great seeing as more people are out, but I also know that some prefer to just catch and not raid.

I think that this Community Day is a great opportunity to use Lucky Eggs and Star Pieces. And depending on where you are and how many are there you could go all out and use Lures and Incense as well.

Personally I haven't decided what to use yet.
I recently reached lvl 40, so I don't really need more XP (though I still chase another million all the time) and I don't have loads of eggs to use.
I will play at a place where I'm sure every Pokestop will be lured all the time and there will be enough spawns so that an Incense won't make much difference, so I suppose I'll hang on to those and Lures.
I will however use Star pieces seeing as I hoard dust.