Hi Pratik
My thoughts only;
1. Prime focus is the way to go and if you already have a DSLR, use it to learn...you might hate astrophotography so at least you will not have a heap of useless gear to get rid of at a great loss.... If you like it then move up to a dedicated CCD after you have produced some nice images with the DSLR.
2. Buy a good compass and a program called "alignmaster" Very accurate polar alighnment in 2 minutes without the fuss of drift alignment. You do not need a camera to use alighnmaster but a 9mm illuminated eye piece is very useful.
3. More then you can poke a stick at. It really depends on the setup you are using. I think an autoguider like the QHY5/orion SS guider is very useful if you plan to do long exposures. (these come with their own software). Oh and a laptop is handy for both 2 and 3
.
4. If you use an off axis guider (OAG) you must take backfocus into account. The orion OAG takes up a fair bit of space (I have one) and adds weight. The more weight you add the better your focuser must be. OAG's are a real pain to use....... It is so much easier to use a seperate scope for guiding and I think Marc's suggestion of a converted finder scope is a good one....bugger all extra weight and you are able to move it around to find a good guide star.
5. Yes I have seen some excellent shots from these scopes. A field flattener will definately help but I dont think the William optics type IV will work as it is made for 3 lens apo scopes. I think the type II is a better choice for doublets....correct me if I am wrong?.
6. 2" EP's only come in longer focal lengths so you will need a combination of both to cover all bases. Main thing is make sure you have a 2" diagonal with a 1.25" adapter so you have a choice of which to use. There is no set formula for this, borrow, beg and steal all the ep's you can and try them in your scope. If it's good, buy one.
Mark