[Sumippi]

'-imasu' is a polite form of '-iru'.

So, '~o tabete imasu'='~o tabete iru', and '~o mite imasu'='~o mite iru', etc.

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Both '~e' and '~ni' can mean 'to ~(destination)'.

I think 'Hachiji ni okite gakkou e itta' and 'Hachiji ni okite gakkou ni itta' are both correct.

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'iki-mashita' is a polite form of 'itta'.(=went)

Both 'Tokyo e/ni itta' and 'Tokyo e/ni iki-mashita' sound OK to me.