You would have to provide chat logs and other means of communications to prove that you both are in genuine relationship and have constant communication especially while being away from each other. Photos and cards/gifts (photos of gifts would do) will also be a big help. Provide as much as you can that will prove everything is real.

Others can give you advice on the financial situation you asked.

We don't usually advice going thru an agency with regards to processing the application. First, it will not be a guarantee of getting a successful visa. Second, you & your wife will still have to gather the documents yourselves and the agency will only collate it. Third, it's actually expensive. Most here did all the processing themselves and most are successful. But if you think your situation is complicated and really need a professional to look into it, and not worried about shouldering the cost of it, then get an accredited agency that will help you. Others might give you some contacts of the ones they know are really good and won't just ask for money money money.