Real Estate Level

Less bit doesn’t make sense, I’m sure you know what I mean

Going from memory... I think 2bn is the max but you don't get anything for it, except for bragging rights I suppose.

You will have to grind and buy tennis courts etc. You get the level then you can store the items. Check the guides, I am sure there is a chart there.
Edit
Found it
https://forums.ea.com/en/the-simpsons-tapped-out/discussion/81718/sh-tables/p1

So if I was to buy one item a hell of a lot, it’s looks as if i should stick to clay tennis courts?

That was what I used. I have hundreds in storage.

@frosted1414 is correct, the cap is 2bn, I made that my mission after I hit the igc cap just for gits and shiggles. Like @Willy9292 I mostly used clay courts but use the tables in the link he posted to utilise all the different currencies to the max. The best mix will depend on which characters you can afford to send on what missions in case you need them for other tasks.
Does anyone know if there's a cap on krustyland tickets? as I'm nearly up to 2 million of those already, it'd be great to max those out if possible.

I'm only about 900,000 KL tickets.