The National Electrical Code does not list a minimum cover requirement for communications circuits, so in theory you could put the conduit at grade level. Irrigation control and landscape lighting has a minimum cover requirement of 6" (150 mm), so I'd probably go with that as a basis.
Since you're not specific about the electric power circuit, I'll discuss a few different situations.
120 volts, GFCI protected, 20 amperes of less
If this is a residential application (which I'm assuming it is, or you wouldn't ask the question), and the circuit is 120 volts or less, and the circuit is GFCI protected, and the maximum overcurrent protection is 20 amperes. The minimum cover requirement is only 12" (300 mm). In this situation, you could bury the electric power at 12", and the communication circuit at 6". This allows 6" of separation, which is likely enough to avoid interference.
Ideally you'll probably want to bury the power circuit at 18", and the communications circuit at 6". Then you'll have 12" of separation, which should be enough to prevent interference.
Over 120 volts, or not GFCI protected, or greater than 20 amperes
If the power circuit is 240 volts, or not GFCI protected, or the maximum overcurrent protection is over 20 amperes. The minimum cover requirement is 24" (600 mm). In this case, you can bury the electric power at 24", and the communication circuit at 6". Then there will be 18" of separation, which is surely enough to avoid interference.
Of the options you are considering, I'd think option 2 makes more sense, and 4-5 feet of conduit - in most cases the conduit will just be continuous from the junction box right through the wall, no particular fuss "as it enters the house" - Come down the wall, put on an LB, drill a hole in the wall, insert conduit, connect to junction box, connect to LB; done. This might be aided by drilling at least a pilot hole from the inside out to make lining it all up easier. Also pick up some duct seal (gray putty, in the electrical aisle) to pack the wires as they leave the LB.
If the wires are entering via an existing conduit, you just need to connect a new conduit to the box that conduit terminates in, and your junction box.
EMT or PVC is six on the one hand, half a dozen the other. I use metal aboveground and PVC below, mostly.
Best Answer
If you're just looking to get a power supply to the shed, you probably don't need to use conduit at all. Steel Wire Armoured (SWA -- roughly equivalent to jacketed/direct bury rated MC) cable is suited to being run underground and doesn't need to be in a conduit. Additional benefits are that it's more resistant to a stray spade trying to dig through it (though if you aim to bury deep enough, that shouldn't be a problem - general guidance is at least 450mm deep, but minimum 2 spades deep should be sufficient) and you don't need to mess about pulling cable through the conduit.
If you want to make it easy to replace the cable entering the shed (should you ever need to), you could use a piece of pipe / conduit / trunking to pass through the concrete base to allow the cable to be pulled easily through.