Tbh mate looking at the parts right.
Gaskets should never be removed then refitted. So dont use a second hand one.
Mounts, for the price and the job they do, best of getting new ones for satisfaction and a peace of mind. Also second hand ones will be hard to come by, and could be buggered.
As the for the sump pan, ok, you could get it second hand, but its a lot of hassle to find one, remove it, post it when it costs £21.
remember those prices are before VAT i think and delivery.
do you NEED all of that? All the mounts?