Problem n. 3: the linguistic situation in Bastarnia.
Just a brief recap, before continuing with historical analysis.
The difficulties are great and the conclusions very tentative, due to the meagerness of the available documentation (not many texts, some hydronymic et sim. data, material culture /notoriously elusive as to ethnicity let alone language!/) Still, decent hypotheses are possible (some much more likely than others).
As of ca. 50 BCE then:
1. The Poeneshti-Lukashovka groups: From the very beginning these incomers (Celto/Germano/"Illyro-Venets"/) existed in a strong Getic environment. and adopted some of its cultural features. We can postulate a growing bilingualism for many, as well as strong original language retention re "Germanic" (whence Strabo's comment), with other original "incoming" languages slowly losing ground. Greek and Iranic would also be known to many as trading (and politically useful) languages. Getic would obviously be reinforced during the ascendancy of Burebista.
2. Zarubinia group 1. Celtic and Veneto/Illyrian would likely hold their own longer (esp. Veneto/Illyrian), as well as Germanic, due to their more even distribution at the elite level, the strength of Veneto/Illyrian among "commoners" (1/2 V/I and 1/2 "BaltoSlavic"), and good contacts with the western Germanic massif. Greek would be much weaker as a trading language here, comparatively (judging by the extant import material, the contacts with the Black Sea coast city states was fairly weak).
3. Zarubinia group 2. The situation here would be closer to the pattern of Poeneshti-Lukashovka. There would be growing bilingualism with the likelihood that Veneto-Illyrian would be more in use at the elite level than Germanic or Celtic, along with the local "BaltoSlavic". Greek and Iranic would be solid trading languages here, and Getic would have some utility in the Burebista period.
4. Zarubinia group 3. The "incoming" languages esp. Germanic would be known, but the primary language would probably be BaltoSlavic. This group's economic ties were primarily to group 32 and to the North. Here BaltoSlavic would also be a trading language.
By and large: P\L and group 1 would be maintaining their linguistic contacts with the Germanic world, while group 2 and 3 would, during this period, be subject to increasing "local" assimilative pressures, but holding their own, less so in the upper Dnipro. These tendencies will become more important in the latter stages of the pre-Farzoi epoch.