You can smoke weed at the time you take the tabs or before, but after you take it is a bit sketchy. People have had unpleasant experiences (myself included) from the combination of psychedelics and weed, as it can be very disorienting. If you do get 25i, don't be freaked out. It's got a bad rep, but it isn't that bad assuming you are responsible with it and don't take more than 1 or 2 tabs. However if you are paying $15 per tab for 25i you are getting ripped off, as it costs like a dollar per tab to make it.
Ehh, this is just my personal experience, but I would much rather NOT be high for the comeup. On one hand, because it's a remarkable thing and worth experiencing on it's own, and on the other, because I would not like already being high, and then having that change, unless I had quite a weed tolerance at the time. I think it's worth experiencing up to the peak on just acid, because it's a special thing on it's own. I have, once, smoked beginning at the time of dropping, and the whole thing was actually a bit weak, though I think they where weak doses. But me and a friend smoked through a fucking eighth of dank during the trip, and neither of us had a massive tolerance at that time, and we didn't get that high...... or trip that hard. And normally that would have been enough weed for us to both have the spins and be marginally conscious. For me, it brings on the trip, but it's not like you're suddenly tripping hard, it's like you're more likely to be hit with a wave of acid, but that wave of acid is less.... acidy. But I've never smoked on a serious dose of acid.
I dislike toking on LSD... it does really disorientate me, but it gives me weird dark visuals that are quite unlike what I have normally. Smoking at t+8 or so, I used to find relatively useful though - it would let me re-live the sequence of the trip and put it back together. Then one time it let me completely re-assemble myself, analysing every aspect of who I am and the choices I've made. As you can imagine, that was quite a rewarding experience. But it still feels rather negative/unpleasant... I prefer LSD on its own - I'm not even a fan of candyflipping.