Are you in the UK, @NewWriter? If so, I'd be inclined to hold off on sending any more submissions out for a little while. You often see advice to send out 30 - 50 queries initially - but that relates to the US. The pool of agents in the UK is much smaller.
It's not an exact science obviously, and it's hard to work out the best way forward, as response times are so slow. There's also the problem that 'no answer means no' has crept in, meaning authors are often left hanging for good. For a first round of submissions, I'd be inclined to stay under 10, give those ones time, and start work on something new.
The risk of sending out a big first batch is that if you get several responses with consistent feedback, those agents are then off the table, since most agents won't re-read, unless it was a very near miss. If it was a smaller batch, you can then decide whether to work on whatever has been flagged up, and then submit a - hopefully - stronger project to the next agents on your list.
The downside of that is, of course, that you could sit around for weeks or months and finish up hearing nothing at all, or just a scatter of form rejections. Or you could get nine full requests and detailed, thoughtful feedback! I do think, however, that it's worth taking a bit of time in the early stages. I don't know how many UK agents are now using Querytracker, but I had a look at some stats/comments on there when I was changing agent, and it's quite useful to see how long each agent typically takes, and whether they have any patterns.
Have you looked at getting any form of feedback on your writing? Unfortunately, personalised rejections - which used to be rare, but not hens-teeth rare - are very much hens-teeth now, with some people even getting form rejections on full requests. It's worth looking at other ways of getting eyes on your work - both manuscript and submission package - rather than holding out for some tiny fragment of feedback from the submission process.