Orbi RBK30 additional satellite advice needed?

Hello everyone, so I have been looking for a mesh system for my home which is a bit larger than normal houses in UK. Its a three story old victorian style terraced house and the virgin superhub 3 just doesn't cut it when it comes to wifi. All these Orbi systems are a bit out of my price range at the moment but I found a package of Orbi RBK30 (SKU: RBK30-100UKS) with a wall plug satellite for around £70 on CCL Computers.

 

My question is if this system doesn't cover the whole house, will I be able to buy another orbi RBS40 AC2200 satellite (not the wall plug one) and connect it to the router of RBK30? Will they connect to each other?

 

2 normal router/satellite system cost £170 and 3 cost £450 here so that's why I was wondering if RBK30 (£70) doesn't solve my wifi issues I can just buy another RBS40 satellite for £130. So that way I will have 1 router 1 normal satellite and  1 wall plug satellite costing only £200 which is better than 1 router and 1 normal satelllite for £170. So what do you recommend?

 

Also on the sidenote, i saw a Linksys wrt1900ac router for £70 somwhere, will that router be better for me than Orbi system?