At what stage would you level up?

My mini city is level 19 (started 2 weeks ago I think, 120k population, 210 storage), and I don't see many Beach/Vu/Storage/Land parts in the GTHQ. On average I see 2 of those parts each time out of 20 listed items.

When the last update came out, there was a flood of beach parts in GTHQ, but it seems Daniel bought most of them, and they soon became rare items again.

The items you'll see will still depend on what the seller is advertising, you just won't see the higher level items that were advertised.

My level 53 city maxed beach since the update came out, as well as increased storage from 250 to 350, and also maxed land. I don't think increasing your level a few times will affect your GTHQ that much.

It doesn't matter how long you wait, you'll always run out of simoleons as soon as you start to climb levels lol. You have to stay active and constantly produce industrial/commercial, and sell on GTHQ (full price) just to stay afloat.

Edit:

Level 17 is a good place to start making serious Simoleons.

Mass produce Nails, grass, and Flour Bags (unlocks at 17), and sell for full price on GTHQ, they have very good profits.