Brokers - Everyone has an opinion, best you can do is pick a few and try them out.
Fees - Depends on your lot size. Commissions are usually per mio, so if you're trading small lots spreads will be more competitive than commissions, and vice-versa.
Spreads - Shop around, there are a few I like but others would not like them for one reason or another. I'm not comfortable recommending specific brokers for obvious reasons.
Platforms - I use a seperate platform for charting and the broker's for placing trades. I like MT4, but most MT4 brokers have poor fulfillment.
Differences - Looked into futures, but haven't traded them. So I don't know.
Volume - There's no volume exchange in forex, that number you see is just some arbitrary tick data calculation. It means nothing, and I've never seen a reliable system take advantage of it.
Liquidity - "Plenty of liquidity" is nonsense. Small trades get executed quickly, big trades still need to find a counter party. The spread represents this.
News trading - Problem is liquidity. You have a lot of ppl that suddenly realize the new immediate direction and pull their counter trades, while a lot of other people jump w/ the herd. So the market becomes highly directionalized and the spread widens to find counter parties. Makes it hard to trade the direct release in a conventional sense, but clever methods still abound.
Taxes - Section 1256 contract. You get a blended capital gains rate, and there's no wash sale rule since it's all mark-to-market. Part of your gains will be your short-term rate based on your tax bracket, another part will be long term. It's fairly nice. Wish all of the tax code was this simple.