If you’re talking about Dusit Thani Laguna, the nearest MRT is Expo on the Downtown and East West lines. There isn’t a station right next to the hotel, so yes, there’s some walking involved unless you taxi or use Grab.
Singapore’s MRT is very efficient. Clean, frequent, easy to navigate. You can pretty much rely on it to get anywhere on time.
For a week, easiest way is just tap a contactless credit or debit card directly at the gates. No need to buy a separate pass unless you really want one. It calculates fares automatically and caps daily spending.
If your conference is at EXPO, you might want to factor in that commute time each morning. Singapore transport is smooth, but the heat and humidity make longer walks less fun than they look on a map.