I know this is a bit of necromancy raising the thread back to life but here's my recommendation for laying out your base.
Ignore that little island of extra nodes in the top right and pretend the guardian is a sentry. I think this would probably be the best layout for your base if your core is still level 4 and you want yet another person's advice.
Like the others suggested, this network creates a choke point at the scanner but also has the security nodes (sentry included) defending each other in case one falls. Just know that there's only so much you can do when having nodes protect each other because of the list of targeting priorities, but at least antivirus will still attack any fallen nodes even if the turrets might be too stupid to turn around. And just as an added benefit, that first sentry will be able to get its antivirus fully installed on the scanner in about 10 seconds because of how close it is and how many secure nodes there are connecting the 2. So unless the enemy is attacking your scanner with level 4+ beam cannons or some other fancy toy, they'll have to drop 2 programs on your compiler just to even take your scanner, you know, that thing that's supposed to be super easy to kill.
Then there's the evolver which isn't connected to the second sentry (whose part tonight is being played by my guardian) so when it falls the enemy has no choice but to attack the code gate directly. No more attacking the code gate on 2 fronts! After the code gate falls I believe the enemy's programs will prioritize your core over that second sentry. Because of how big the core's firewall is and you having 2 nodes shooting antivirus at the code gate, you'll be able to retake the code gate at if they neglect to use an ice wall. So either they waste the time (and programs which are precious with only 1 library) retaking the code gate for having failed to protect it or they do in fact allocate a program slot to an ice wall further limiting the number of offensive programs that can go on it and in turn reducing their damage output against your core. Either way it'll buy you some more time. Remember that you don't have to have a totally impenetrable defense, just one that runs out the clock.
The rest is about resource node arrangements and is largely irrelevant and likely doesn't deserve to be in this thread but I ramble:
Broadly speaking, when it comes to arranging business nodes there's 2 approaches: run to the hills and rally the peasants. The former calls for you to have your business nodes be as far in the back as possible and be connected to as few other nodes as possible resulting in strings or branches maybe up to as much as 3 nodes long (or deep for you CS people out there). By scattering them like this you protect your resources better from a kraken attack (centralized resource clusters are usually located near the core so krakens clear the way right to them) and waste as much of your opponent's time and beam cannons as possible while they try to hunt down each and every node. Its weaknesses are worms which easily spread out across a network if given the space and just a short amount of time as well as beam cannons if the attacker still has some left in reserve. This is more common at higher levels once you actually have a large enough network to properly scatter these nodes. The other strategy is to have all of your business nodes interconnected so they can protect each other with antivirus. This works well if the attacker has little to no programs left, particularly ice walls or shuriken; however, be warned, if your opponent has brought the kraken with them then you'll want as few nodes connected to the core as possible because once the kraken consumes the core it attacks all nodes directly connected to it at once, wiping them out in a matter of seconds (the silver lining is that it travels no farther).
At your level though it's rare to be attacked by anyone with krakens (expensive to train and require a level 5 core with expensive research) or the program capacity to have numerous programs lying around after breaking through all of your security (2 program libraries, again, only obtainable with a level 5+ core) so I'd go with the second approach and place the core right in the middle of that web of business nodes using all 5 of its connections if possible. But if you find yourself under attack from krakens more and more often as you level up you could try forming the chunk of business nodes without incorporating the core into it and placing the choke point node of the cluster (the only one connected to anything outside the web) in one of 3 possible for this network. The first location is right behind the core, this is done by connecting the choke point node only to the core so the cluster would only have one node within reach of a potential kraken and would remain safe until even after the core falls. The next anti kraken resource arrangement would be to sever the connection between the code gate and the core and place the choke point node in between the 2; however, this would likely interfere with the list of targeting priorities that would have allowed the second sentry to go unnoticed while the core was under attack. The final and arguably the best of the anti kraken business node locations would be to attach the choke point node to the second sentry as it would likely fall after the core anyways and because that sentry would never be attacked by the kraken and the sentry has multiple available connections, it could be woven into the resource cluster and even act as the choke point node.