Advice on my dying Dlink modem and our upcoming fibre

Hi all

So we have a Dlink 2888a modem which has served us well the past couple years with VDSL. Lately it seems that the 2.4ghz wifi is dying as we can connect to it but get no internet working, it might not be giving out an ip?? 5ghz still works fine. I have tried factory reset etc. Also seems every week or two i need to reboot it to get the internet connection running again.

In the next couple months we should finally get fibre installed (its in the street now, our area in small town must be the last to get livened up)

I dont know much about fibre as I have never had it before, but I understand we just need a router with it.

Our house is 3 levels, so I currently have the modem in the middle of middle floor, a bridged old spark HG659 I think down in the garage, and ethernet running to a couple of Nvidia Shield tvs, and a laptop plex server, security cameras etc and consider our 5 person home on the heavier side of usage, maybe 600gb a month

So my question is, do I make do with my Dlink modem for the next few months, and then get a router from slingshot when we connect to fibre? Or is that likely to be insufficient for wifi coverage? As it is the Dlink struggles to get to one end of the house upstairs, and it wasnt perfect downstairs (hence the bridged modem below it)

My other thought was buying a TPLINK AX6000 router $600 now and using it once we have fibre as well, but didnt want to waste money at this stage if I dont have to.

Thanks for any opinions or advice