Not advice but useful info which may help.
You tend to get a better recline on the 0+ seats rather than the combination ones.
It is useful to be able to carry them around in the seat or get them sorted in the seat before you leave the house. And leave them in it if they are asleep. Yes - not great for safety, but OK as long as total length of time in seat (in and out of car) does not exceed 2 hours in one go (30 mins for first 4 weeks.)
We still decided on a 0+/1 for the next stage because I liked it better than any of the other options, and it wasn't any more expensive. DH miffed that "we could have used it from birth" I said yes, but you insisted on the "clicky thing" (car seat base/pushchair adaptor combo). We decided on one which can do forward and rear facing. I just wanted the chance to rear face longer than the infant carrier allows. I think after 2 or so I will probably be more laid back about FF and not mind so much, but I just wanted to keep our options open personally.
If you plan to have a second baby within 4 years, it's likely they will also need use of a 0+/1 seat at the same time - you get an extra 9-18 months' leeway (allowing for smaller gap without doubling up on car seats) or even longer if you decide OK - will move DC2 into 0+/1 seat, and buy 123 seat (booster with removeable harness) for DC1 at say 2.5/3ish. NB this also goes for those car seat bases which boast you can use for both car seat stages.
If you have a child who happens to be larger than average (unfortunately antenatal scans aren't a good predictor of this) and/or you want them in more protection than a booster seat longer than a Group 1 seat will allow (most children outgrow these at 3.5-ish - a child who is large for age, 2.5; only small-for-age children get past their fourth birthday) you may later want to buy an extended harness or extra-large rear-facing seat - these are worth purchasing immediately at the end of Group 0+ usage, rather than waiting for them to outgrow Group 1 and then getting a Group 2 EH/ERF, since all of these seats also cover Group 1 and are just as if not more expensive. Whereas any Group 0+ seat will fit all newborns (you might need a specially small one for a prem baby), delaying the point you decide on a Group 1 (which may include Group 0+) vs a Group 1/2.
Bear in mind if you want a base for your infant seat for convenience (click in and out of car, no fiddling with seatbelts) these are sometimes more expensive than the seat 
I'd always recommend factoring in the cost of both parts, when comparing. Also in addition to the one base/two seats issue with 2 DC I mentioned before, most Group 1 seats don't need a separate base, just the ones that go with these one base/two seat systems - it is a marketing ploy to keep you loyal to that brand for Group 1.
Although i-size uses height limits rather than weight, all seats currently available still use the same rough categories for sizing, so it's useful to stick to the same terminology. 90% of car seats are outgrown by height/physical size before weight anyway so take the weight limits with a pinch of salt.
We have just moved DC2 up to a RF Group 0+/1 - he doesn't seem to mind at all, he has a much better view up there as the seat is higher. Little children are often more comfy RF because it means they have a place to rest their legs so they don't dangle over the edge and go to sleep. I always found it exciting to be "the wrong way" as a child.
Here's an album showing a child right at the limit of Group 1 in various rear facing seats, first all Group 0+/1 seats, and the last 2 are Group 1/2 ERF seats. Some have more leg room than others, but this is the top limit for the seats - most of them also have FF option so you could switch.
www.facebook.com/pg/RearFacingToddlers/photos/?tab=album&album_id=701900873287098&ref=page_internal
I think in hindsight I'd have got the cheapest infant carrier/base combo that is compatible with pushchairs (IIRC, Joie Gemm + Gemm base/i-base, but may vary if you find a good offer). Then I'd have used that for 6 months or so and looked into whether to change to a Group 0+/1 or Group 1/2 (if the latter, you need to use the infant seat to capacity).
One last point - not all 0+/1 seats are allowed to be used rear facing until age 4. When you are comparing seats checks this - an R44 certified seat will state that it can be used rearward-facing up to 18kg (but some have lower limits of 13kg or even 10kg) and an i-size seat will usually have a rear facing height limit of around 105cm, but some of them have a smaller height limit of about 86cm, which most children will reach by 18-24 months ish.
Sorry :o Way too much info as usual but hope some of it is useful... feel free to ask if you have more questions.