You are a US citizen correct? I'm assuming that you are, but correct me if I'm wrong. Okay so there are a few moving parts to the questions you asked me, I'm going to do my best to explain it all and then feel free to ask me if you have any additional questions.
You have 2 options, to either get legally married in India and then file for a green card as a spouse, OR file for a fiance visa and then you have 90 days to get married once he gets to the US.
For applying for a spouse-- once you have what's referred to as a bona fide marriage in India, ie. it's not a sham and you do it all legally and legitimately, you can file for his green card. There's no priority waiting list for the spouse of a US citizen, so what that means is he's guaranteed to get it, he just has to wait for the processing time.
For applying for a fiance-- you apply for him, the local Consulate in India will then send him an interview date, he goes in for the interview, and generally gets the visa handed to him that day if he is approved. Then he travels to the USA, and you have 90 days to get married.
As far as wait times go, I can't give you an exact time as it varies depending on how busy USCIS is and how much they get backed up on their applications. It also depends on how busy the Consulate is over in India when trying to schedule him an interview. What I can do is give you some general estimations of the usual wait times. When applying for a spouse, the general wait times can be 4-6 months on the fast end, and up to 12-18 months on the very slow end. Fiance visas tend to run similarly in the 4-6 month range, and around a year on the very slow end. Although you should keep in mind that these visa applications are generally processed on the faster end, I just want you to have a full picture of all the possibilities.
As far as traveling, you are still allowed to travel outside of the US to India at any point in time during this process. The only thing you need to know is that when you eventually fill out the Form I-964 form, which is the Affidavit of Support which USCIS requests after they receive your application, you need to show that you do reside in the US and have the intention of continuing to do so in the foreseeable future. This can be done through showing a permanent US mailing address, copies of your income taxes, proof of a US bank account, etc.
I hope that helps! I know it's alot of information so please let me know if you have any other questions. Also please take a moment to rate me using the stars, as this is the only way the experts are compensated for our time here on 'just answer'. It does not cost you anything additional to rate me, and we can still continue our conversation for free after. Thanks!