1) No. There is not a one to one relation between a job in Tridion and a job in your TMS (translation management system in general, not SDL TMS specifically).
A job in the TMS will always belong to a single job in Tridion, but one job in Tridion can have multiple jobs in the TMS.
The split is done if the job gets too big, or it can happen if not all files need to be translated to the same set of target languages.
The latter can happen if you select to not translate items that are already translated. If you want to translate two items to German and French, but one (and only one) of them is already translated to German you will end up with one item being translated to French only, while the other item is translated to both languages. Translation Manager may split the job into two in this situation. If it happens or not will depend on the TMS used and internal implementation in Translation Manager. We reserve the right to change how Translation Manager split jobs - it could even happen in a hotfix (normally not, but we will not consider this a breaking change).
You can configure the maximum size in the configuration files. But please do consider that it is important to keep an efficient translation process so always consult with someone understanding the translation process before making significant changes.
2) No. Once Translation Manager has used the bundle to resolve which items to translate it will not use the bundle information for anything. The items from the bundle will be distributed over TMS jobs as any other items added to the job.
3) You can use a Machine Translation developer account on SDL Language Cloud. It won't let you see the exact files being send as you could if you had your own SDL TMS or World Server, but you can get content translated. There is a limit to the number of free translations you can perform on a developer account, but there should be enough for you to play around with. Notice earlier versions of SDL Tridion refers to this as SDL BeGlobal while SDL Web 8 use the new name SDL Language Cloud.