To resize a partition during staging, you need to drag and drop the partition from Source to Destination, then select it in the Destination section and click "Cloned Partition Properties" to specify a new size, as demonstrated in Steps 4 and 5 of that KB article I linked. If the partition you want to extend is the last partition on disk, then technically you could do this afterward, but sometimes people have one or more Recovery partitions after their C partition, in which case you need to extend beforehand, otherwise you'll have one or more Recovery partitions sitting between your C partition and the free space you wanted to allocate to that partition. In the latter case, you have to resize your C partition on the destination BEFORE dragging down any subsequent partitions, so just set the new size to a value that leaves enough space for any remaining partitions you'll need to drag down. Reflect allows you to specify a partition size either in terms of actual size or how much free space to leave after it, which is a helpful capability here.
In terms of MBR vs. GPT, that won't be automatic, but Macrium has a KB article for a custom restore mechanism that will address that here
. So your full plan here will be:
1. Follow Steps 1-10 of the MBR to GPT custom restore KB article, i.e. the section for how to prep your custom disk.
2. When staging the restore, follow the steps in the cloning KB article I linked earlier, taking care to a) drag and drop all partitions from the source to destination, working left to right, and b) preserve the existing two small partitions on the destination that you'll have created just beforehand. Again, remember to resize your C partition at this point.
3. If this isn't already the case, make sure that before you proceed, you are booted into Rescue Media on your new PC, that your clone source disk is disconnected, and that your new disk is connected. Also make sure that you are booted into Rescue Media in UEFI mode, which you'll be able to tell by checking the title bar at the very top of your Rescue Media. If it says "[UEFI]" at the end, you're good to go.
4. After the restore completes, run Fix Boot Problems.
5. Run ReDeploy.