Is Parent / Child Theme scalable with Multisite?

Hi

I am looking to set up a multisite network, where people can register for a website – like WordPress.com

Due to the nature of my users specific needs (I will be aiming towards a niche target audience), I want to have the themes custom made for me. Each theme would have the same functionality in the back end, but I wanted to give the users different theme styles to choose from.

There will be some custom post formats, and maybe custom post types, fields and/or custom templates.

On the surface, a parent / child theme setup would appear to be perfect for this. I can put the functionality I require in the parent, and just have the different theme look and feel using child themes.

But, will it scale up?

I know that the wordpress code can scale to many concurrent users, but will a parent theme? My concern is that if I used the parent/child theme setup, then every site will be drawing off the one parent theme. Will it lag or just plain fail if it gets too many requests at once?

I am talking about getting the parent (and children) custom made for me, and not using a bloated theme framework. I will specifically ask for only the code required and no overlaod.

I don’t know who would write the code yet. I have used elance for programming projects in the past, and would probably try finding someone on there again.

Thanks,

Paul