The most important thing is to enjoy your riding. If you don't enjoy it, you won't keep doing it and as far as I'm concerned, a year of happy riding is better than deciding it's all too hard and painful after a month or two.
I'm just coming out of a quiet month. It started with an impressive prang at 30km/hr (face first onto bitumen - the term 'ouch' was used repeatedly). Apart from letting the various bits that hurt stop hurting, I also found I wasn't as keen to rush out into dark nights and cold rain as I'd been earlier. Nor did long rides have much appeal. So I just did a few quiet, slowish rides and now, a bit over a month later, I can feel a return of the urge for more extravagent riding (ie, my son rolls his eyes and tells me I'm insane).
But yeah, a HR monitor is a fun toy and a very useful tool. You won't regret buying one.
Richard
107 kg, not proud of it but not ashamed either