You can get steeringwheels in basically all categories ranging from very cheap (under a 100) up to very expensive (over 2000).
If you are a casual racer and this is your first game I'd pick one in the first category. If racing is your passion but aren't full time occupied with it go for a mid-range steeringwheel and if you are an over the top simfanatic that spends countless of hours of racing go nuts and buy an expensive one.
T300RS opened up a whole now chapter in driving versus my old G27. Coupled with the CSPv2 pedals you cannot want more (ok, forget about the new 1500+€ wheels). Will you be using it mounted on a racing rig?
Everything is possible, you just need "some additional money to spend". This can be done with F1 TS wheel if you decide to buy T300RS. And regarding the space needed to mount a wheel to your desk, fear not since T300 is a nice small package, i have it mounted on regular desk and i'm a little short with space too.
Especially since Fanatec's prices went up recently. But if you can, grab a set CSP v2 pedals.
On the other hand, you will stop getting out with your friends, spending money on things that aren't simracing related, ...... so you spend some and you save some.
The G27 is fantastic value, good enough +1. I currently have a Fanatec Forza CSR and twice its been in the shop for repairs, but when it comes back from the shop and I feel those effects, its definitely another level from the G27.
I have the CSR Elite pedals, and even though I've had to repair those, I would buy them again. Given another chance, I would get the T500RS set. I'd bet the T300 is good if pair with pedals with a clutch.
As an owner of a Thrustmaster TX...I say you should go with the G27 for now until you become a complete sim racing addict. That way, when you upgrade to a higher end wheel you will have the G27 as a very nice back-up.
My set up - Thrustmaster TX, Fanatec CSP V2 pedals, F1 add-on wheel, GTE add-on wheel, TH8RS shifter, Fanatec Classic rim on DSD Thrustmaster Hub adapter (this is for the classic cars ). A set of Fanatec CSP V1s as back-up and T3PA Pro pedal set on order.