Yes the Sonesta Taba is actually just outside.... Nuweiba. It should be a good 45 km or more to Taba itself at the border, but just 20 km from Nuweiba. A taxi from Nuweiba to the border costs LE 150 - 250 ( and during very busy times up to LE 300 ). From the Sonesta it will be more or less the same as it is a major hotel and isolated.
From the Sonesta to Dahab will be about 95 km but expect to have to pay only slightly more than for Taba. Add 50 % more if you want him to wait 2 - 3 hours for you.
There is no Duty Free shop at Dahab - but there is one at Nuweiba Port ( which has its own little town around it along with banks, a few shops, bus station, etc ) and which is 6 - 7 km south of Nuweiba Town, which has more shops and that. You can buy imported alcohol and that from the duty free shop within 24 hours of your arival - i.e. the same day or the day after as they just look at the date of your arrival and not the exact time. The Nuweiba duty free does not have a very good choice of stock but they are the most flexible of all the duty free shops in Egypt ( even allowing purchases in LE !! ) - but you must take your passport with you.