We have just return with my mum from Roma.
The flat is very clean and comfortable.
Bus is 30 sec- 1 minute/ 2 different stops/. During our stay stop Stradivari worked only on Sundays. so please check but it does Not matter because you have other options. Tram stop is 5 min.
From Fimuchino airport take train to Trastevere station and the 7-8 min walk or bus/ train.
In the flat there is everything you could need + some coffee capsules.
10-15 min by public transport to the center.
To Vaticana museums take train to Valle Aurelia train stop+ Metro for 1 stop. Metro station is 2 min from train station.
To San Pietro basilica again with train but to San Pietro station. Ticket is 1 Euro.
It is very easy.
When you watch Vaticana museums and reach Sistine capella before the exit there is a door on the right that leads to the basilica and no need to go out and wait again.
It was a nice stay in Roma.