A sitar has movable frets, a row of sympathetic strings under the playing ones, and a bridge whose curved surface produces the instrument's whole character. Nothing on this page is transferable from a guitar, which is exactly why it exists.
These are explainers, not a catalog. No prices, no brands, no reviews: this site has not handled the instrument you are considering and will not imply otherwise. What it can tell you is what to look at, in what order, and which jobs belong to a specialist rather than to you.
Where to start
If you do not own one, start with your first sitar — most of the instruments offered online are ornaments, and the tells are easy once you know them. If you own one and it has stopped resonating, read strings first. If it sounds thin or rattly rather than quiet, that is a jawari question, and setup is the page.