Welcome, yuvan, to FT. Your question is somewhat general and does not include enough specific info to allow a really specific answer. But let me take a shot at helping.

First, you will not be able to get credit for all those miles flown in the past, at least as far as I am aware. No one that I know of allows mileage from before you signed up with any specific affinity (DL, US, AMEX, Starwood, etc.) card to be counted - only miles accrued and dollars expended AFTER you sign up.

Second, you need to look at focusing on one airline or one airline group (e.g. SkyTeam, StarAlliance) as your vehicle for achieving miles and points and award flights. In general, you will need to accrue $20-25K spending on any general credit card to be eligible for a domestic (USA) award flight. You asked about $10K spending getting you 10K miles of free travel but the general rule is you must have at least 25K points in any given airline to qualify for a domestic USA return flight award no matter what the actual flying mileage of that flight. There are occasional specials that allow you to fly for less than 25K points but they are rare. As just one example, if you were to get the Starwood AMEX card and use one of the sign-up sites referenced frequently here on FT you would be receive 10K points on that card upon your first purchase with the card. You would then need only 10K more in purchases on the card to have a total of 20K and you could then transfer those Starwood points to a wide variety of airlines (excluding AA and UA as well as some others) and get a bonus 5k in the transfer, giving you a total of 25K in points with whatever airline you chose. This 25K could be used for a domestic round trip (USA) on that airline, assuming award availability. Thus, you would have to spend only $10K on your credit card to be eligilble for a potential award ticket on a given airline.

There are many, many other options open to you but I'm afraid you'll have to do a lot more homework on your own reading the "stickies" in more detail with regard to each airline to find out what option may be best for you. Look at what airline/alliance you would use most out of your home airport and find a card that aligns with that reality. Sorry I couldn't provide more specific options but this should get you started. Good luck and, again, welcome to FT.