You are really not leaving much time to spend in Lisbon which is a lovely city.
While you are there you must see at a minimum the Castelo São Jorge from where you will get a great view of the City, the Praça do Comercio, Jeronimos Monastery and Belem. Also the town and Castles at Sintra.
I think you will find the IBIS Saldanha not great for parking and a lot of traffic. When I drive up from Lagos to Lisbon we usually head to the IBIS Malhoa at Avda. Jose Malhoa. This has easier access to the ring road with routes to the Algarve over either one of Lisbon's Bridges.
Parking is easier there as well. You can go round the back of the hotel where there is free parking. The Metro Stations at Jardim Zoologico and Praça de Espanha are 5-6 minutes walk away and give great access to the rest of the city. You should walk or take public transport as you will see nothing by driving.
As regards travelling to the Algarve by car be warned we are now entering the hot season. The inland route to the Algarve through the Alentejo will be hot. I always try to leave at this time of year (going either way) early morning circa 07:30 to miss the worse of the traffic in Lisbon and teh heat in the Alentejo. The Coastal route can also be hot.
Note the Motorway is a toll road from Lisbon until you get to the Algarve A22 motorway.
If you want to take the scenic route I recommend leaving Lisbon on the Motorway and coming of just past suitable a Marateca. Once on the old National Road IP1 follow the signs for Alcacer do Sal and Grandola.
Option 1
At Grandola you can go right to Sines and then follow the coast road through Vila Nova Milfontes to Odeceixe, Aljezur and Lagos.
Option 2
Continue on through Grandola until you pass Mimosa. (Stop for a coffee and a break at the first cafe on the left.) Just after Mimosa you will find a road signed to the right indicating Lagos. Take this and you will eventually wend you way to coast road mentioned above.
Option 3
Another 25 km further there is another road to the right marked Odemira. Take this and pass through Odemira following the signs for Odeceixe, Aljezur and Lagos
Option 4
Continue down the IP1 towards Albufeira. You will intersect with the A22 coastal Motorway. Bear right and continue 60km till you get to Lagos.
On the return you could follow the coastal route to Sines and from there follow the road to Troia and take the ferry over to Setubal. From there you are only 40 km from Lisbon.
There is a great IBIS at Setubal as well with garden and pool. A nice place to relax after a days drive.
