Planes games can be low level and starting in sigil is a good idea. Here's an excerpt from the wiki if you haven't read it.
Sigil is located atop the Spire in the Outlands.[15] It has the shape of a torus;[15][16] the city itself is located on the inner surface of the ring. There is no sky, simply an all-pervasive light that waxes and wanes to create day and night. Sigil cannot be entered or exited save via portals; although this makes it quite safe from any would-be invader, it also makes it a prison of sorts for those not possessing a portal key. Thus, sometimes Sigil is called "The Cage".[17] Though Sigil is pseudo-geographically located "at the center of the planes" (where it is positioned atop the infinitely tall Spire), scholars argue that this is impossible since the planes are infinite in all dimensions, and therefore there can never truly be a center to any of them, let alone all of them; thus, Sigil is of no special importance. Curiously, from the Outlands one can see Sigil atop the supposedly infinite Spire.
So starting in the Outlands would be a great place for some low level adventures, since the Outlands are like a pseudo material plane, with snippets of every other plane in it, but very stable. I imagine it like a giant ring with different climates and obstacles and such contained in huge sections, but the divide between each is completely sudden. Like a snowy field cuts to an immediate grassy savannah. At least that's how I imagine some of it