What should I upgrade to get better speed?

Hi

I have Spark Fibre100 but on a SpeedTest I only get 38 Mbps down and 12 Mbps up. This is far cry from what the Fibre is theorectically capable of. I am thinking about upgrading the equipment to get the most out of the Fibre, but preferably in a piece meal fashion so not to spend a large chunk of money in one go.

Current set up:

ONT -> Huawei HG659b (Wifi AP disabled, used as a router / wired switch only) -> Unifi AC LR in the middle of the house.

The above speed test was done using Wifi on my iPhone standing right next to the Unifi AC LR.

Also from the above HG659b:

(1) to a 10/100 Powerline Ethernet adaptor via powerline to another 10/100 Powerline Ethernet adaptor -> TV

(2) to an old HP Laser Jet JetDirect network card

(3) to an old HP OfficeJet

So to get better speed to better utilise the Fibre100, shall I:

(1) Swap the Huawei for an EdgeRouter ER X, with Eth1-Eth4 put on Switch0 to connect the Unifi (via PoE), the two printers and the Powerline?

(2) Get a switch to put between the Huawei HG659b and the various bits (Unifi, printers and powerline)

(3) Change some settings somewhere on my Unifi or Huawei?

What kind of speed should I be expecting with an optimised setup, using Fibre100?

Thanks