Hi,
About Azure free trial account limitations, please refer to below links:
http://www.windowsazure.com/en-us/offers/ms-azr-0018p
If you want to know what reached the limitation, you can contact our support for more info, forums members can not provide offcial answer about your azure account:
https://support.microsoft.com/oas/default.aspx?gprid=14928&st=1&wfxredirect=1&sd=gn
About billing question, if you use free trial account, please careful about resource limitations, "If you exceed these allocations, a spending limit will apply and your service will be disabled until the beginning of the next billing month".
If you want to use Pay-As-You-Go account, here you can find billing details:
http://www.windowsazure.com/en-us/pricing/details/
I think Windows Azure 6 month deal may more suitable for stable, mature applications and services, and it will help you save more, here is these two deals:
http://www.windowsazure.com/en-us/pricing/purchase-options/
For Medium Size Virtual Machine you need pay for $115.20 per month, Small size Virtual Mahine for $57.60 per month. (From Azure Caculator).
Hope this helps.
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