  Quantum information processing with neutral atoms relies on Rydberg
excitation for entanglement generation. While the use of heavy divalent or
open-shell elements, such as strontium or ytterbium, has benefits due to their
optically active core and a variety of possible qubit encodings, their Rydberg
structure is generally complex. For some isotopes in particular, hyperfine
interactions are relevant even for highly excited electronic states. We employ
multi-channel quantum defect theory to infer the Rydberg structure of isotopes
with non-zero nuclear spin and perform non-perturbative Rydberg-pair
interaction calculations. We find that due to the high level density and
sensitivities to external fields, experimental parameters must be precisely
controlled. Specifically in ${}^{87}$Sr, we study an intrinsic F\"orster
resonance, unique to divalent atoms with hyperfine-split thresholds, which
simultaneously provides line stability with respect to external field
fluctuations and enhanced long-range interactions. Additionally, we provide
parameters for pair states that can be effectively described by single-channel
Rydberg series. The explored pair states provide exciting opportunities for
applications in the blockade regime as well as for more exotic long-range
interactions such as largely flat, distance-independent potentials.
