35 l is about 10 us gallons. I wouldn't add any more fish to it until you upgrade.
Go with the largest tank you can afford and fit; an 80l at least, which is about 20 US gals. Not a huge upgrade but it'll give you a few more options. If you can go larger though I would.
I've upgraded tanks before without issues. Just either move the filter media from the current 10 gal filter into the new filter or run the 10 gal filter on the new tank for at least a month with the new filter. This will instantly cycle the tank for the fish you have now. When you add new fish, do it slowly and test water daily and do extra water changes as needed until the bacteria catch up (you might see a temprorary ammonia and/or nitrite spike).
For moving the tank, this is how I've done it:
--Get a clean Rubbermaid type bucket (make sure it's food grade as some used for outside will have pesticides in them)
--Siphon out the water from the 10 gal into the bucket; leave enough water for the fish.
--catch the fish and put them in the bucket; add the current heater to the bucket and if you can run the filter on the bucket, do that. if not, just add an air stone in the bucket if you have one. Keep the filter media wet in old tank water
--Lid the bucket so the fish won't jump out
--Finish draining the current tank; take out decorations, plants etc you wish to move (you can put the plants into the bucket with the fish).
--Move the old tank.
--Set up the new tank. Fill it up. Add the new heater.
--Add the new filter (with filter media from the current one or add the 10 gal filter to the new tank along with the new one)
--Let it run until the water gets up to temp
---Net the fish into the new tank
--Keep the lights off and don't feed for the first day until the fish get used to their new surroundings
