What is the average wind speed with you? Unless you are fairly light you'll need VERY high wind to use a 3.3. I'm 85kg and need around 18 knots to use my 4m - I reckon it's sweet spot is 20-25 knots for me. A 5m is perfect for my weight in 15-20 knots - I could hold them in a fair amount more wind but it just gets uncomfortable and the more overpowered you are the quicker you tire.
It depends on your skill level, but especially as a beginner, if you go for too big a gap you'll have a range in between the two wings that one hasn't got enough power while the other has too much power. Having said that I wouldn't have though a 1.7m gap would be impossible - I'm sure you can hang onto the 5m until there's enough power for the 3.3m to take over (they are fairly easy to depower), but unless you live in an area which is blessed with LOTS of wind (or you are very light), you might be better going for a slightly bigger wing than a 3.3m. Other sizes you could consider are a 3.6m (I think f-one does this size) to pair with your 5m, or if you go for a 4m you could pair it with the Naish s25 5.3m. It really depends on your weight and the wind conditions you'll be using them in. We mostly get very light wings here so I have a 7m, a 5.3m, and a 4m for the odd time when it blasts, but if I had to get rid of one I would drop the 4m simply because i don't get to use it as much as the others because of the wind conditions here.
Gong do a chart that gives guidance for wing size/wind range/rider weight that could be useful, but I think that some of their estimations for the smaller sizes are a bit optimistic, especially for beginners - I'm not sure I'd want to hold onto a 3m in 57 knots!!!!!!! See the link for the chart - scroll to near the bottom of the page and click on 'Buying Guide':
https://www.gong-galaxy.com/en/product/gong-wing-pulse/