I'm just curious how hard an override of the veto to restart the
goverment is?
Very hard.
It requires 67 votes in the Senate (assuming that there are no vacancies at the time and no one fails to vote) and 290 votes in the House (making the same assumptions), i.e. two-thirds majorities in each house. The one vacancy in the House doesn't change the required number of votes.
Democrats have 47 seats in the Senate to 53 Republican seats, so they need 20 Republican votes to override a veto in the Senate. This is more than a third of Republican Senators.
Democrats have 235 seats in the House to 199 Republican seats (with NC-9 vacant due to election fraud). So, Democrats need 55 Republicans to join them for a veto override in the House. This is more than a quarter of Republican Representatives.
Of course, they need to have these majorities in both the House and the Senate, not just one of them.
are there enough liberal republicans for that to be possible, or would
more hardliner republicans be required?
There have never been fewer moderate Republicans (and there is no such thing as a liberal Republican in Congress, almost every Republican is more conservative than almost every Democrat) than they are right now, in recent history (certainly not since the 1960s). One would be hard pressed to identify five in the Senate who fit that description, when twenty are needed, and likewise there aren't anywhere near 55 moderate Republicans left in the House.
The marginal Republican in the U.S. Senate based upon one conservative to liberal scale ranking is roughly Sen. Dan Sullivan (R-AK), the junior Senator from Alaska. The marginal Republican in the U.S. House is roughy Rep. Elise Stefanik (NY-21).
The partisan divide in the House is actually deeper than it is in the Senate.
The amount of ideological difference between Democrats and Republicans in Congress has never been greater in modern history.
Also, differences on a liberal-conservative dimension between red state and blue state Democrats and between red state and blue state Republican, have almost completely vanished in recent years (see the chart below) so the distinctions between red state and blue state Republicans suggested by the question are pretty much irrelevant. Moderate Democrats have been replaced by Republicans and moderate Republicans have been replaced by Democrats in a process called "realignment" that has almost completely run its course as of 2018 with only a handful of exceptions.
The charts above only go through 2014 and 2015 respectively, but the trends illustrated continued in the 2016 and 2018 elections. Moderates in both parties were disproportionately replaced in those elections. (The trend is likely to continue into 2020 as well as those members of the Senate who have announced an intent to not run for reelection or to consider not running for reelection are more moderate than their caucuses as a whole.)
In short, it would take a massive revolt by Republicans in Congress to override a Presidential veto. At this point, nothing close to this much dissent within Republican ranks has materialized, but that could change over time.
