Are their going to be any problems with me being a Fighter/Barbarian/Dervish if my attribute are the following? Str 16; Dex 16; Con 18; Int 15; Wis 14; Cha 14. Should I make my Dex 18 and my Con 16 instead of how it is listed?
I don't know how your DM decides how stats are figured, but those seem like some across the board really good stats. If any stat should start off an odd number, I like to make it Strength since carrying capacity is affected by an exact STR score, while everything else works off stats at the even numbers. But that's just me.
When should I get the combat expertise, expeditious dodge , mobility, weapon focus (scimitar) and the two-weapon based feats? Should also go to level five of Tempest? The Dervish handbook list as of the gold standard for whirling Dervishes. Swashbuckler 3 / Fighter 2 / Dervish 10 / Tempest 5
You should get those feats whenever you intend to have them before whatever level you plan to take the Prestige class. Are you playing this character in a game starting at level 1? is this an NPC in a game in which you're the DM? In all the times you've built characters, I still have no clue how your DM works, how your games work, how you play in any way, if you build characters for writing, or if for you this is all a mental exercise (which is ok and cool if it is, I develop theoretical builds for fun).
Sometimes taking feats in a particular order end up making an awkward PC during those middle levels while you're on your way to becoming the awesome level 20 build. If I know your starting level and how the character will progress, I could give clearer suggestions. If you're starting at level 12, 17, 20, etc, it matters a little less what order you take the feats in.
Without that information, I'm not sure a truly helpful way to advise you, and you've never answered any of the questions I've asked in the past about such things.