  We report on NICER X-ray monitoring of the magnetar SGR 1830-0645 covering
223 days following its October 2020 outburst, as well as Chandra and radio
observations. We present the most accurate spin ephemerides of the source so
far: $\nu=0.096008680(2)$~Hz, $\dot{\nu}=-6.2(1)\times10^{-14}$~Hz~s$^{-1}$,
and a significant second and third frequency derivative terms indicative of
non-negligible timing noise. The phase-averaged 0.8--7~keV spectrum is well fit
with a double-blackbody (BB) model throughout the campaign. The BB temperatures
remain constant at 0.46 and 1.2 keV. The areas and flux of each component
decreased by a factor of 6, initially through a steep decay trend lasting about
46 days followed by a shallow long-term one. The pulse shape in the same energy
range is initially complex, exhibiting three distinct peaks, yet with clear
continuous evolution throughout the outburst towards a simpler, single-pulse
shape. The rms pulsed fraction is high and increases from about 40% to 50%. We
find no dependence of pulse shape or fraction on energy. These results suggest
that multiple hotspots, possibly possessing temperature gradients, emerged at
outburst-onset, and shrank as the outburst decayed. We detect 84 faint bursts
with \nicer, having a strong preference for occurring close to the surface
emission pulse maximum the first time this phenomenon is detected in such a
large burst sample. This likely implies a very low altitude for the burst
emission region, and a triggering mechanism connected to the surface active
zone. Finally, our radio observations at several epochs and multiple
frequencies reveal no evidence of pulsed or burst-like radio emission.
