I think it really depends what level you’re at: If you’re already at a high playing level, with an excellent command of proper feel, phrasing and ornamentation, then you could learn as many tunes as you had time for, and you’d know well enough when you could play them well.
OTH, when you’re pretty new to the music, I think one is far better off concentrating on learning one tune really well, before moving on to the next. Certainly while playing and improving the tunes you already play.
That’s been my experience anyway; I went through a period where I learned a number of tunes, and could play them by wrote, but they just never sounded or felt quite right, even though the notes where there. It’s all too easy to memorize the series of notes, that make up a tune, and then move on, without ever really getting the proper nuances of phrasing, rhythm, apropriate ornamentation, breath, and playing in time. There are all too many examples of this on clips and snips - no offense intended to anyone, as this has been pointed out by far better players than myself, on numerous occasions.
Take the time to learn one tune well, REALLY well. Get some help with this, from someone experienced in ITM if at all possible. I can’t stress this highly enough. If this not possible, for whatever reason, you must rely on critical listening - record your playing, and compare it to that of good players, well respected players. Don’t worry about the speed difference, I gaurantee that if you are really playing a tune well, that tune will sound fantastic even at the slowest tempo - It will still have drive and lift, it will make others want to tap their feet, and the tune will sound “right” regardless of the tempo.
Now, I’m off to practice, and rather slowly, in fact. 
Loren