Since you are looking for satellite conjunctions you will want good accuracy. The values in TLEs are intended only for use by an SGP4 propagator, and not designed to be used in other ways. You can get very approximate results by using them directly, but the results will be incorrect, and you won't be able to tell how incorrect they are!
For example while a simple method might work for crude sorting purposes, a lot of old satellites in graveyard orbits (and those that lost control before making it there) will be cruising very close to GEO with substantial inclination and/or eccentricity and/or creeping along longitude non-synchronously. A simple method to guess positions from TLEs will turn out to be not so simple, and may still miss some particularly interesting cases that may turn out to be the ones you are looking for most!
There are many sources for SGP4 propagation out there (the right way to do it), in many computer languages, but I don't know if there is one that is written in R and also well tested and supported.
I would recommend you try to learn a bit of Python if you don't know it already. I use Skyfield as an easy way to SGP4-propagate TLEs. See How can I plot a satellite's orbit in 3D from a TLE using Python and Skyfield? and also here for example.
I know that for Python there is the Python Package Index or PyPI: https://pypi.org/ which is a central index to search for packages. I noticed that it doesn't include Skyfield (because SGP4 is just a small part of it) and it also fails to show https://github.com/brandon-rhodes/python-sgp4 However, it does show Poliastro https://pypi.org/project/poliastro/ which might also work well for you.
If you know of a similar index of packages or software for the R language, then you can try searching for various combinations of the words
Two Line Element Set
propagator and of course