You had one long crank? COuld be just moisture in the tank.
DOn't change any parts yet until it's more systemic.
To answer your questions, I do not think a clogged filter would result in a long crank. You'll first hear the fuel pump straining to maintain fuel pressure before a long crank. Old plugs? Maybe, but you should get it every crank if they are old (or at least much more often).
2002 A4 1.8T M/T quattro
APR Stage 1, snub, TIP, 710N DV
Neuspeed Short Shifter
Koni FSD/Eibach/H-sport S4 sways
B5 S4 front brakes, Porterfield R4S
Stoptech SS lines
Dunlop SP Sport 01/Yokohama AVID H4S