What is the max span that can be supported by 2x4 floor joists?
I’m American so I don’t understand the metric system, but I’ll try to answer.
When you ask for the maximum span of a 2x4 floor joist at 12” on center, there are many issues. We design from the top down and build from the bottom up.

Your subfloor must be rated to span from joist to joist. If you use 12” spacing then a 1/2” thick board is acceptable, but at 16” spacing you should use 5/8” plywood and for 24” spacing then use 3/4” thick plywood.  This is based on supporting 15 lbs. per square foot of Dead Load and 65 lbs. per square foot of Live Load. (This is higher than normal, but will allow you to use a tile floor without deflecting too much.)

The maximum span for joists depends on species and grade. I’ll assume an average grade of Number 1 (C16). C16 is economical to use and easy to find. So, for 2x4 at 12” oc the maximum span is about 7’-6”, which is about the distance you need. (If you go to C24 it could be longer.) Remember, spans are measured from face of support to face of support.

Joist hangers are also rated. Finding a hanger that will accept a true 2” wide joist will be difficult. Simpson has a hanger and is rated for 600 lbs., which is fine for your application.

Using a perimeter ledger could require a 2x6, because you need 4 times the bolt diameter. A 1/2” bolt would require an edge distance of 2”. A 1/2” bolt will need to be about 12” on center to support your load.