Talk to me about Design Constraints - Textures, map sizes, lighting

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Hi, just getting started in Photonland and have some questions from the design side:

How big can I make my level maps?
All projects I have demoed are very small and compact. When I build a quick project/game to the cloud, I find it very "snappy", like very quick to respond. Like tons of memory left... is that because only 1 player?
I guess what I am asking is should I make mini levels or can I make big 4K square terrains with high texture resolution? And if I want to do that is there anything I should consider for lighting setup? Thanks in advance...