Not exactly. "Хохман" would be more equivalent to "Chochmann" in German.
A bit of both. Russian doesn't have the
sound represented by "h" in English, German, etc, so a lot of early loanwords from those languages were spelled with "г", because that's apparently what the Russians of the time thought was the closest sound in Russian to the /h/ they heard in English/German/whatever. More recent loanwords tend to be borrowed with "х" (which certainly sounds more like /h/ to English speakers than "г" does, and given that English doesn't have the
sound represented by Russian "х" or German "ch", you don't even have to worry about an English speaker confusing [h] and [x]).
Neither German nor English pronounces "h" when it has a vowel before it and a consonant after it, as in "Hohmann", so "Hohmann" could be transcribed in Russian as either "Гоман" or "Хоман". (Also, in German, an h following a vowel tends to indicate vowel length, so you could even transcribe it "Хооман").
In IPA, the German pronunciation is /hoːman/.
The English pronunciation (my dialect) is /homɪn/ (speaking quickly) or /homæn/ (speaking slowly), though most English speakers would probably say /homən/ for the fast-speech form. /o/ in English is generally more exactly pronounced as [əʊ] or [oʊ], so in the end you'll get something like [həʊmən] or [həʊmæn].
Note: In discussing pronunciations, linguists tend to use quote marks (eg, "may") to talk about how something is written in a language, slashes (eg, /me/) to talk about the sounds that native speakers perceive, and brackets (eg, [mɛɪ]) to talk about the details of the actual sounds that are produced in an utterance.