I'm planning on using:

2 or 3 buckets of Xanthan gunge
A couple of cartons of custard
Half dozen eggs
3 tins of spaghetti
Honey
Maybe some cooking oil?

This is my first time, if this too much or a great way to start?

Use whatever feels right to you.

I recommend people start small to avoid getting overwhelmed. Maybe just try some eggs and spaghetti OR the gunge, custard and oil for your first time.

Duly noted. Thank you for the advice.

Out of interest, what would be overwhelming?
Not being a dick, genuinely interested.

I wouldn't want to ruin my first time.

Those are wonderful ingredients for the first time

Just be able to clean up and watch out for overflow

Variable. It could be surprising how messy the session could end up, and how much cleanup could be required. That, or the smells and sensations could be different from what you expect. Hard to predict!

I eased myself in using single cake or pie slices.

As it's your first time, I think it's great of you to throw yourself into it. That being said, I think anyone who's been at it a while will agree that the size of the clean-up strategy should match the mess.

Speaking with 40 years experience of getting messy: don't overdo it at first. The feelings will be wild and intense, right from the very first moment. It probably won't take very much before you achieve a fairly mindblowing orgasm. And then you have the cleanup. If you've used way more than actually needed, you'll then have way more work to do, which might spoil the experience.

Use enough to have serious fun, but don't use so much the work part of dealing with it afterwards overwhelms the pleasure part.

Sounds pretty ambitious. I'd echo the other comments to start small and then scale up from there in the future. Cleanup can be a bitch if you have too much stuff, so definitely plan for that ahead of time. Ideally, you'd use a little of something at first to gauge its complexity, and then work from there.

In that vein, the more water-soluble your substances are, the easier cleanup will be. For example, using honey or syrup is likely easier than xantham gum, which takes effort to mix evenly and could potentially clog a drain if not diluted sufficiently before disposal.

Besides the feeling, the smell will likely be the most unexpected thing your first time. It's something which is more intense than you'd anticipate. For that reason, I'd probably avoid mixing sweet and savory at first until you've experienced them individually.

Some things you may want to have around are garbage bags to toss stuff, wet (paper) towels to wipe your eyes (burning eyes from sugar or acids are a turnoff), potentially tarps to cover surfaces, and a bottle of water (especially if you go big, cleanup can be a decent amount of physical labor).

Also make sure to be comprehensive with your cleanup. Don't forget places like behind your knees and ears, as well as the bottoms of your feet and between your toes, all places that mess can hide.

All of that being said, there's a certain charm to how new and unexpected certain things will be that you can only experience the first time before planning and experience get in the way. Enjoy it!

Thank you all for your comments and advice which I will certainly consider carefully.

I'll keep you posted.

What is this "too much" you refer to?

In all seriousness, the mess to clean grows exponentially, not linearly. So go easy until you have a good idea of how to clean up after yourself.

It can also get overpowering in terms of smell too; Xanthan is pretty neutral, but custard and spaghetti both have strong smells which get a lot stronger when you start messing with them.
Similar thing with the texture of eggs (especially with the shells).

I'll echo the opinions about not overdoing it at first- if it's something you've fantasied about for a while you'll probably come pretty quickly.
You can set the extra mess up ready (it's still tonnes of fun even when you're spent), then if you decide to finish early you're set for a later session this weekend.

I was going to say this same exact thing.
I remember when I first started? I did an entire 32 gallon trash can, to the brim of cake batter.
While it was soooo fucking fun and I would LOVE to recreate it.now that I have some different ways and help with disposal. When I first did it? I laid some tarp down. I had NO IDEA what I was in for!
It took me and some neighbors to get it all bagged up and we had lots of large spills and crazy shit go down!
Needless to say my wam adventures were outed to my neighbors. they didn't care but yeah it was nuts!
Now? The list you have seems pretty reasonable! Just get you a 2ml tarp and maybe put it in your bath tub. Once you are done? Have a garbage can close by to put anything that won't go down the drain and let the tub do the rest!

Have fun!