Will you be arriving in Vancouver in mid-March or later in the month? Rental cars don't always have the best tires for driving in winter conditions and at that time of year, there could certainly be snow in the Whistler area. The Sea-To-Sky highway seems to have regular MVI's so you'd need to drive very carefully.
I agree with a previous comment that it's not a good idea to stay in the Gastown area. I'd suggest staying more in the centre of the downtown area in the vicinity of Burrard & Georgia Streets. There are lots of nice hotels in that area, Pacific Centre mall and lots of nice restaurants along Robson Street. Most hotels seem to charge for parking.
I assume you'll be visiting someone in Abbotsford, as there's not really a lot to see in terms of "tourist attractions" in that area. I don't know of any "resorts" in that area, other than Harrison Hot Springs which is some distance from Abbotsford and on the other side of the Fraser River. How many days are you planning to stay there?
One word of caution.... traffic on Highway 1 from Abbotsford and back to Vancouver can be extremely congested at certain times of the day, with bumper-to-bumper traffic and moving only a short distance at a time. You could use the older Lougheed Highway route on the other side of the river and go across to Abbotsford via the bridge at Mission or the Golden Ears bridge in Maple Ridge.
What to do in Vancouver..... there are lots of options. Some that come to mind are Stanley Park, the Capilano Suspension Bridge, Grouse Mountain, Granville Island and the Art Gallery is right in the downtown area. You could also try the Sea To Sky gondola or the Britannia Mine Museum on your way to or from Whistler. You may have already looked at this website - https://www.destinationvancouver.com/?gclid=EAIaIQobChMIx8fUroXs-wIVygqtBh3hxQOiEAAYASAAEgJiivD_BwE&gclsrc=aw.ds . One night in Vancouver is not going to allow much time to see anything, so you won't have any trouble finding activities for the few hours you'll have for sightseeing.
One note about Stanley Park.... the Park Board has just voted to remove the bike lane that was put in place during the pandemic. The bike lane used one of the traffic lanes, so that now opens the park up to normal vehicle access.