Looking to the future

Whilst I'm awaiting my fist brew kit to arrive (dry kit, extract and a bag of hops) I've been looking at where homebrew might lead me and planning a 'road map' of progression.
Assuming the kit works I'd like to move onto some of the other recipies that I've seen here using extract.
My quetion is about the boil pan volumes and also about boil pans. The recipe that comes with the kit I've got says about 1 Gallon should be okay for making up 5 gallons of brew. I'll link the instructions here:
drybeerinstructions

This is more than likely going to be okay for this recipe but some of the recipes on here either don't mention the boil volume or specify larger than 1 gallon, eg 3 gallons. I don't have a pan this big so will I have to invest in a BIG pan?

If I do go for a BIG pan how big should I go? What If I want to move onto all grain or partial mash? I looked at This is how big your Mash Tun needs to be and it suggests 5 Gallon tun would be ideal

As a final question, I'm struggling to find these really big pans. Most of the time I'm looking they consider 10L to be big, but I get the feeling that that won't be big enough. Any hints on good search terms?
I'm a bit strapped for £££ at the moment, so a good cheap solution would be best.

Sorry if this has been covered elsewhere.

As most people will say here, go as big as you can and that your equipment will allow. Even with extracts, the closer you can get to a full boil, the better. The real issue more than likely what your burner situation is. Many stoves will have a hard time getting 4 or more gallons to a boil, or at least take a very long time. That alone will limit the size boil you do.

As far as recipes are concerned, you can offset the smaller boil volume by doing a late extract addition. This will allow you to get your hop utilization pretty close to what the original recipe calls for.

To give you an idea, I use a 5.5 gallon pot and use 4.5 gallons of water + extract. That gives me about 2 inches of head room and after boil off I only have to top off with a little more than half a gallon to get me to the 5 gallon mark after the boil.

I don't know what your shopping options are across the pond, but my pot mentioned above is stainless and cost around $40 at a typical department store.

I've had a good look around thus far and the best balance between cost and size appears to be this:
4 piece stainless steel stock pot set: Amazon.co.uk: Kitchen & Home

And the biggest pan it comes with is 20L (4 gallons) would this be suitable for most brews?

For doing extract brews a 4 gallon pot should be fine. Just use 3 gallons of water for your wort and add the rest of the water later. But if you ever wanted to move onto all grain I would suggest something larger.