Can someone please help me clarify what this person is saying?
 

I'm sorry I realize this is not a translating site and I should try to translate this myself, but I am completely confused.

"わかりました。
じゃあひらがなでかきますね。よろしく。"

My best guess is this: "Understood. So, hiragana police (I am going and coming back) politely end. Nice to meet you."

I looked up each individual part on several different question and answer sites and that is what I came up with.

Wakarimashita= Understood.
Jyaa= So
hiragana= hiragana
deka= police officer
kimasu= going and coming back
ne= polite/friendly way to end a sentence
yoroshiku= Said when meeting someone for the first time, unsure of exact English equivalent but I was told "Yoroshiku onegaishimasu" meant 'Please treat me favorably and I will treat you favorably.'

A fairly admirable try, but I sense you don't have much experience with japanese. I would translate it as 'Understood. Well then, I'll write in hiragana. Pleased to meet you'.

So, I'm gonna go out on a limb and guess you're talking to a Japanese pen-pal of some sort and you told them you either can't read Kanji or don't need romaaji. Yoroshiku onegai shimasu is what you'd say when you request a favor of someone usually (there's lots of other ways to say this, but it's not important right now). It's also said the first time you meet someone, so I tend to translate it (in this context) as 'Pleased to meet you'.

Kimasu 来ます（きます） is actually not 'go and come back'. It's just 'come'. 行ってきます is something you would say when you leave your house that literally is like 'I'll go and come back' but can be very loosely translated in english as just a goodbye when you leave the house.

Finally, デカ is probably not police officer specifically. I've got some very minor experience with police terms (thanks to 逆転検事), I'd translate it as 'detective'. Granted, I've never asked for a native's opinion on this, but my dictionary also gives me 'detective' instead of 'police officer'.

Sorry my post is so long, just wanted to explain some stuff. :)

Just to back up Duo's translation, I'm going to add a not that you split the words in the wrong place, it's
wakaremashita, jyaa, hiragana, de, kakimasu, ne, yoroshiku.
Hiragana+de= 'in hiragana'
kakimasu= to write.

Excuse the romaji, I'm at work and it takes me longer if I have to swap inputs all the time.

Yes, you are very right. They asked me (in English) if I understood Romaji, Hiragana, Katakana, and Kanji. I told them I could 'understand' all except for Kanji.

So can jyaa be translated as a sort of concluding word or phrase? ex. So, well then, in that case, given the information ect.

どもありがとうございます～！

Oh I was afraid I would do that. =/ Okay, that makes a lot of sense now.

どもありがとうございます～！

The word is どうも、not ども. Romaji influence?

If it is, will it be taken as an opportunity to decry the uselessness of romaji and your corresponding superiority in other Japanese written forms?

This undercurrent of fragile elitism I'm seeing is really beginning to grate on me.

No doubt, I say death to romaji (err, I am mean the Roman alphabet being used in Japanese)

Well, considering he is a native speaker... I am not so sure what he is being so elite about.

And being against romaji has nothing to do with showing off one's Japanese ability. People who are against are mostly likely against it because they know that in the end it is nothing more than a hindrance to learning the Japanese language effectively and properly.

Uhh sorry. Does it looks less unintellegent if I just write "Domo arigato gozaimasu" and pretend I've learned nothing?