Hi,
I think the best is to look at some statistics book for HEP or follow some tutorial on statistics, like the CERN academic trainings that are recorded.
But in brief, answering your questions:
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more data you have will make the log-likelihood narrower and you will get smaller uncertainties, but the central values of the parameter will not change significatly
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The rule -2Ln L + 1 applies to likelihood ratio (log-likelihood differences) and not absolute likelihood values.
The likelihood values vary a lot experiment by experiment. See for example this notebook:
https://github.com/lmoneta/stat-course-ipmu/blob/master/Session2/LikelihoodAsGoF.ipynb
Lorenzo