Is it good to buy all scenic trips/excursions in advance such as Schilthorn , Matterhorn paradise, Gornergrat, Jungrau etc or better to buy it on spot ?
Secondly, which websites sells all the excursions because "http://www.swissrailwa ys.com/en/excursions " is selling few only.
There's no need to buy them in advance, but you can if you want to. It's advisable to only buy the ones you will be visiting for sure in advance. The weather may not be suitable, and there's no point in going up if the top is covered in clouds. If you buy through the website you mentioned you will get open date tickets so you're not tied to a specific day. They will ask you for a date when you buy, but that's only the first day you can use the ticket.
Indeed not all tickets are available online. If they are, there's a link in the price section of our attraction pages: Schilthorn, Gornergrat, etc.
So wont be there long queues ?
That greatly depends on the date, time, place and weather. So it's hard to predict. It's low season from now to mid-December, so in most cases it should be alright.