Bonus is 50 seats to biggest party, 250 seats are awarded roughly proportional. So 100+ seats are needed from proportional distribution if the coalition includes the largest party, 150+ if the coalition does not include the largest party, ie 40+% or 60+%.

In the last three polls you get roughly these percentages (average by quick look):
Pro-austerity
ND 29
Pasok 5

Anti-austerity
Syriza 33
ANEL 3
KKE 6

Nazi
XA 7

Other
Dimar 1
Potami 7
Other 9

To enter parliament, you need 3% so Dimar - anti-austerity in election, then in pro-austerity government, then leaving government but collaborating with them - is gone. Looking at the EP election, the other is a varied collection of 1-2% parties so absent surprises those can be discounted. With 10% not represented, the amounts needed falls to 36+% and 54+%. So perhaps Syriza and ANEL (if they keep their numbers above the threshold) or Syriza and KKE.

Potami appears according to wikipedia (en, fr, de) to be some sort of lofty pro-European party that is heavily dependent on celebrity leader. They are members of the S&D group, but not PES. Socialliberal, but left and right is no good guide to pro- and anti-austerity in Greece. With their numbers and right-left position they should be natural partners for Syriza if they are anti-austerity. So are they anti-austerity?

Deutsche Bank apparently thinks so:

Deutsche Bank predicts victory of SYRIZA and coalition government with POTAMI | protothemanews.com

According to Deutsche Bank, following the unsuccessful election of President of the Republic, which by the way was to be expected, a new era of political uncertainty opens up which raises three main questions. What will be the reaction of Europeans in early elections, who will win the election and what approach the new government will follow?

Among other, the German Bank attempt to answer to the above questions and predicts concerning the elections, a victory of SYRIZA and coalition government with POTAMI.

(I haven't watched the video there.)

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