Thailand is a country, like India. Where in Thailand do you want to go to? There are direct flights from Delhi to Phuket and Bangkok, so I'd suggest you choose either or. Will share some recommendations once you've made up your mind on which place would you like to go to.
HI I will say it would be great experience to travel by own.
ya Thailand is beautiful place no doubt . If your planning with Family then better don't go to PATTAYA walking street area.
you can go to JOMTHEN BEACH it's at PATTAYA but very different and more clean less crowd . here is some suggestion for family travel.
BEACHES HUA HIN / KOH SAMUAI / KHARBI / JOMTHEN. HILL STATION BEST IS
CHING MAI / CHING RAI IN BANGKOK AREA TO AVOID with family .
NANA / SUKUMVIT 03 / NANA PLAZA / KHAO SAN ROAD . STAY IN BANGKOK SUKUMVIT 15./14/
SUKUMVIT 11 IS OK TOO.
SILOM
Hi. Great choice. 2-3 nights sufficient for Bangkok and it has budget hotels and great beaches. Cheap flights from air Asia or Indigo. You will like the Bangkok zoo...it's the best I've seen. you can self book para sailing and other water activities. all available on site after bargain. Use metro for local travel. Next 2 days sufficient for Pattaya. Walking street and night market is good. you won't need any agent. Self book flights and hotel and visa is on arrival so carry documents and as soon as you land,visa formalities can be completed at the airport itself. please feel free to connect for further questions.
Since you want to go to Krabi, take a direct Indigo flight from Delhi/Mumbai to Phuket. You can stay around Patong Beach areas. You can get a decent hotel at approx 4k/night. There are day trips from phuket to phi phi/james bond island which you can take. Feel free to ask anymore questions.