Yes, it is just around the corner from you. 3 minutes by foot. Come out of the hotel, walk down the street, first right and you are there.

It's a matter of personal preference. Portomaso is closer to the buzz of St Julian's and Paceville (nightlife, restaurants and what watersports there are). Sliema is more of a business centre as well as residential. It has more shops and is generally quieter, but does nevertheless have good restaurants. I don't know Tigne Point very well, but it is very modern and seems very expensive and a bit soulless (probably much quieter than Sliema itself). Parts of the Sliema Ferries/Waterfront area can have great views of Manoel Island and Valetta, and is a pretty lively area.

It is located at he mouth of the marina, just below the swimming pools of the Hilton. It is expensive and I think that you can taylor your journeys at a price. I don't think that you can land at Valletta. A day bus ticket costs 1 euro, 50 and you can travel the whole island on that ticket. Valletta bus station is just outside of the old town's walls and is a hop,skip and a jump into the town. We found that due to the large crowds waiting for busses to arrive, we caught a taxi back to St julians 20 euros well spent when you were tot and tired.